U.S. patent number 6,432,475 [Application Number 09/456,912] was granted by the patent office on 2002-08-13 for pressure-sensitive adhesive composition, process for the preparation thereof and pressure-sensitive adhesive sheets.
This patent grant is currently assigned to Nitto Denko Corporation. Invention is credited to Tomoko Doi, Fumiko Kamifuji, Yutaka Moroishi, Kenichi Okada, Michiharu Yamamoto.
United States Patent |
6,432,475 |
Yamamoto , et al. |
August 13, 2002 |
Pressure-sensitive adhesive composition, process for the
preparation thereof and pressure-sensitive adhesive sheets
Abstract
A pressure-sensitive adhesive composition having well-balanced
pressure-sensitive adhesive force and cohesive force without
causing any safety or economy problems, a process for the
preparation of the same and pressure-sensitive adhesive sheets
using the same are disclosed. The pressure-sensitive adhesive
composition comprises a crosslinked polymer obtained by
crosslinking a block copolymer comprising at least two of a
styrene-based polymer block A and an acrylic polymer block B having
a structural unit represented by the general formula
(1):--[CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 ]-- wherein R.sup.1
represents a hydrogen atom or methyl group, and R.sup.2 represents
a C.sub.2-14 alkyl group, bonded each other, such as A-B or B-A
type block copolymer and A-B-A type block copolymer.
Inventors: |
Yamamoto; Michiharu (Osaka,
JP), Moroishi; Yutaka (Osaka, JP), Okada;
Kenichi (Osaka, JP), Kamifuji; Fumiko (Osaka,
JP), Doi; Tomoko (Osaka, JP) |
Assignee: |
Nitto Denko Corporation (Osaka,
JP)
|
Family
ID: |
27474314 |
Appl.
No.: |
09/456,912 |
Filed: |
December 7, 1999 |
Foreign Application Priority Data
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Dec 8, 1998 [JP] |
|
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10-348335 |
Jun 16, 1999 [JP] |
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11-170220 |
Aug 6, 1999 [JP] |
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11-223149 |
Oct 29, 1999 [JP] |
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11-308230 |
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Current U.S.
Class: |
427/208.4;
428/413; 428/500; 428/523; 525/94; 526/145; 526/146; 526/147;
526/320; 526/93 |
Current CPC
Class: |
C08F
293/005 (20130101); C09J 153/00 (20130101); Y10T
428/31938 (20150401); Y10T 428/31855 (20150401); Y10T
428/31511 (20150401) |
Current International
Class: |
C08F
293/00 (20060101); C09J 153/00 (20060101); B05D
005/10 (); B32B 027/30 (); B32B 027/32 (); B32B
027/38 (); C08L 053/00 () |
Field of
Search: |
;428/413,500,523
;526/135,145-147,93,320 ;427/208.4 ;525/94 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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5403658 |
April 1995 |
Southwick et al. |
5754338 |
May 1998 |
Wilson et al. |
5763548 |
June 1998 |
Matyjaszewski et al. |
5807937 |
September 1998 |
Matyjaszewski et al. |
6274688 |
August 2001 |
Nakagawa et al. |
6288173 |
September 2001 |
Schimmel et al. |
|
Foreign Patent Documents
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0 298 667 |
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Jan 1989 |
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EP |
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0 921 170 |
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Jun 1999 |
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EP |
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2 267 284 |
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Dec 1993 |
|
GB |
|
Other References
Polymer Science Dictionary; Mark Alger, Chapman & Hall; 1997:
Cure and Crosslinking.* .
European Search Report..
|
Primary Examiner: Dawson; Robert
Assistant Examiner: Feely; Michael J
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A process for the preparation of a pressure-sensitive adhesive
composition, which comprises subjecting a styrene-based monomer and
an acrylic monomer represented by the general formula (1A):
CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 wherein R.sup.1 represents a
hydrogen atom or methyl group, and R.sup.2 represents a C.sub.2-14
alkyl group, to a living radical polymerization in an appropriate
order of monomers using a polymerization initiator in the presence
of a transition metal and its ligand to produce a block copolymer
comprising at least two of a styrene-based polymer block A and an
acrylic polymer block B bonded to each other, and then subjecting
said block copolymer to crosslinking to produce a crosslinked
polymer, wherein said styrene-based monomer and said acrylic
monomer are subjected to a living radical polymerization together
with at least one monomer selected from the group consisting of a
monomer having an epoxy group in its molecule and a monomer having
a hydroxyl group in its molecule.
2. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 1, wherein said block copolymer is
an A-B type or B-A type block copolymer.
3. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 2, wherein said styrene-based
polymer block A is present in an amount not exceeding 50% by weight
based on the total weight of said block copolymer.
4. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 1, wherein said block copolymer is
an A-B-A type block copolymer.
5. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 4, wherein said styrene-based
polymer block A is present in an amount not exceeding 60% by weight
based on the total weight of said block copolymer.
6. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 1, 2, 3, 4 or 5, wherein said block
copolymer contains a hydroxyl group in its polymer chain and is
heat-crosslinked with addition of a polyfunctional isocyanate to
the hydroxyl group.
7. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 1, 2, 3, 4 or 5, wherein said block
copolymer contains an epoxy group in its polymer chain and is
irradiated with ultraviolet rays with addition of an onium
salt-based curing catalyst thereto to epoxy-crosslink.
8. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 7, wherein said block copolymer
contains at least two epoxy groups per molecule.
9. The process for the preparation of a pressure-sensitive adhesive
composition as claimed in claim 8, wherein said epoxy groups are
incorporated in said block copolymer at or in the vicinity of the
end of the polymer chain thereof.
10. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 7, wherein said block
copolymer contains at least one epoxy group and at least one
hydroxyl group per molecule.
11. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 10, wherein said epoxy
groups are incorporated in said block copolymer at or in the
vicinity of the end of the polymer chain thereof and said hydroxyl
groups are incorporated in said block copolymer at or in the
vicinity of the polymer chain thereof.
12. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 7, wherein said block
copolymer contains at least two hydroxyl groups per molecule and is
epoxy-crosslinked with addition of the onium salt-based curing
catalyst and an epoxy-based crosslinking agent to the hydroxyl
group.
13. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 12, wherein said hydroxyl
groups are incorporated in said block copolymer at or in the
vicinity of the end of the polymer chain thereof.
14. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 1, wherein said transition
metal is Cu, Ru, Fe, Rh, V or Ni and its ligand is a bipyridine
derivative, mercaptan derivative or trifluorate derivative.
15. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 14, wherein a combination
of said transition metal and said ligand is Cu.sup.+1 -bipyridine
complex.
16. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 1, wherein said
polymerization initiator is an ester- or styrene-based derivative
containing a halogen in .alpha.-position.
17. The process for the preparation of a pressure-sensitive
adhesive composition as claimed in claim 1, wherein said
polymerization initiator contains an epoxy group or hydroxyl group
in its molecule.
18. A process for the preparation of pressure-sensitive adhesive
sheets comprising preparing a pressure-sensitive adhesive
composition by subjecting a styrene-based monomer and an acrylic
monomer represented by the general formula (1A):
CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 wherein R.sup.1 represents a
hydrogen atom or methyl group, and R2 represents a C.sub.2-14 alkyl
group, to a living radical polymerization in an appropriate order
of monomers using a polymerization initiator in the presence of a
transition metal and its ligand to produce a block copolymer
comprising at least two of a styrene-based polymer block A and an
acrylic polymer block B bonded to each other, and then subjecting
said block copolymer to crosslinking to produce a crosslinked
polymer, wherein said styrene-based monomer and said acrylic
monomer are subjected to a living radical polymerization together
with at least one monomer selected from the group consisting of a
monomer having an epoxy group in its molecule and a monomer having
a hydroxyl group in its molecule, and providing a layer of the
pressure-sensitive adhesive composition on a support.
Description
FIELD OF THE INVENTION
The present invention relates to a pressure-sensitive adhesive
composition comprising a crosslinked polymer obtained by
crosslinking a block copolymer comprising at least two of a
styrene-based polymer block A and an acrylic polymer block B
block-bonded each other and a process for the preparation thereof.
The present invention also relates to pressure-sensitive adhesive
sheets of the pressure-sensitive adhesive composition in the form
of sheet, tape or the like.
BACKGROUND OF THE INVENTION
In recent years, pressure-sensitive adhesives such as solvent type
pressure-sensitive, emulsion type pressure-sensitive adhesive and
hot-melt type pressure-sensitive adhesive have been used for
materials which are required to be easily adhered by simply
pressing, such as packaging pressure-sensitive adhesive tapes,
masking pressure-sensitive adhesive tapes for coating, sanitary
pressure-sensitive adhesive tape, paper diaper fixing tape and
pressure-sensitive adhesive label.
As the solvent type pressure-sensitive adhesives there have been
known acrylic and rubber-based pressure-sensitive adhesives. In
recent years, it has been required that the amount of
pressure-sensitive adhesives to be used be minimized from the
standpoint of drying efficiency, energy saving and working
atmosphere. If the amount of the solvent to be used in the
polymerization is reduced to meet this demand, a safety problem
occurs due to difficulty in controlling the resulting
polymerization heat. Further, the emulsion type pressure-sensitive
adhesives are disadvantageous in that since they comprise polymer
particles dispersed in water, the water content needs to be finally
removed during the formation of the pressure-sensitive adhesive
layer, resulting in the deterioration of drying efficiency and
energy saving.
The hot-melt type pressure-sensitive adhesives are superior to the
solvent type or emulsion type pressure-sensitive adhesives with
respect to safety or economy. For example, hot-melt type
pressure-sensitive adhesives mainly comprising styrene-isoprene
block copolymer have been known. In general, however, this type of
pressure-sensitive adhesives exhibits a poor light resistance and
thus are disadvantageous in that the resulting products exhibit
deterioration in properties with the lapse of time. In an attempt
to overcome these difficulties and hence obtain pressure-sensitive
adhesives free from these difficulties, acrylic polymer components,
which are normally known to exhibit a good light resistance, are
introduced instead of the isoprene-based polymer components, which
cause the deterioration of the light resistance of the resulting
products.
A random copolymer of acrylic monomer with styrene-based monomer
can be easily synthesized. There are examples of an
pressure-sensitive adhesive mainly comprising such a random
copolymer. However, no products exhibiting satisfactory
pressure-sensitive adhesive properties have been obtained. On the
other hand, block copolymers of styrene-based polymer component and
acrylic polymer component cannot be easily obtained by any of
radical polymerization method, anionic polymerization method and
cationic polymerization method. There are no examples of a
pressure-sensitive adhesive mainly comprising such a block
copolymer.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a
pressure-sensitive adhesive composition which comprises as an
pressure-sensitive adhesive a block copolymer of a styrene-based
polymer component and an acrylic polymer component that has been
easily produced free from safety problems in the absence of solvent
or in the presence of a small amount of a solvent to satisfy the
desired pressure-sensitive adhesive properties in addition to the
inherent characteristics due to the introduction of acrylic polymer
component, i.e., enhancing the light resistance, without causing
economic problems as in the conventional emulsion type
pressure-sensitive adhesives, i.e., problems in drying efficiency
and energy saving due to removal of water content.
Another object of the present invention is to provide a process for
the preparation the pressure sensitive adhesive composition.
Still another object of the present invention is to provide
pressure-sensitive adhesive sheets comprising the
pressure-sensitive adhesive composition.
As a result of extensive studies on the above-described problems,
it has been found that a living radical polymerization of a
styrene-based monomer with an acrylic monomer in the presence of a
specific activating agent and a polymerization initiator makes it
easy to produce an A-B type or B-A type block copolymer or
three-block or higher copolymers of styrene-based polymer block A
and acrylic polymer block B, no appropriate synthesis methods of
which having been known, in the absence of a solvent or in the
presence of a small amount of a solvent without causing any
problems in controlling the resulting polymerization heat. It has
also been found that the use of a crosslinked polymer obtained by
crosslinking the copolymer as a main component of a
pressure-sensitive adhesive makes it possible to obtain a
pressure-sensitive adhesive composition which sufficiently
satisfies the desired pressure-sensitive adhesive properties,
particularly well-balanced pressure-sensitive adhesive force and
cohesive force and excellent heat resistance, in addition to the
effect of enhancing the light resistance characteristic to the
acrylic polymer block B without causing any economic problems as:
in the conventional emulsion type pressure-sensitive adhesives. The
present invention has been completed based on those findings.
The present invention provides a pressure-sensitive adhesive
composition comprising a crosslinked polymer obtained by
crosslinking a block copolymer comprising at least two of a
styrene-based polymer block A and an acrylic polymer block B having
a structural unit represented by the general formula (1):
--[CH.sub.2 --C(R.sup.1)COOR.sup.2 ]-- wherein R.sup.1 represents a
hydrogen atom or methyl group, and R.sup.2 represents a C.sub.2-14
alkyl group), block-bonded each other.
The present invention also provides pressure-sensitive adhesive
sheets comprising a layer of the pressure-sensitive adhesive
composition having the above structure provided on a support.
The present invention further provides a process for the
preparation of the pressure-sensitive adhesive composition, which
comprises subjecting a styrene-based monomer and an acrylic monomer
represented by the general formula (1A):
CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 wherein R.sup.1 represents a
hydrogen atom or methyl group, and R.sup.2 represents a C.sub.2-14
alkyl group, optionally together with a monomer having an epoxy
group in its molecule and/or a monomer having a hydroxyl group in
its molecule, to a living radical polymerization in an appropriate
order of monomers using a polymerization initiator in the presence
of a transition metal and its ligand to produce a block copolymer
comprising at least two of a styrene-based polymer block A and an
acrylic polymer block B, block-bonded to each other, and then
subjecting said block copolymer to crosslinking to produce a
crosslinked polymer.
DETAILED DESCRIPTION OF THE INVENTION
Details of the living radical polymerization method are described
in various literature references, e.g., (1) Patten et al., "Radical
Polymerization Yielding Polymers with Mw/Mn .about.1.05 by
Homogeneous Atom Transfer Radical Polymerization", Polymer
Preprinted, pp. 575-576, No. 37 (March 1996), (2) Matyjasewski et
al., "Controlled/Living Radical Polymerization. Halogen Atom
Transfer Radical Polymerization Promotedbya Cu(I)/Cu(II) Redox
Process", Macromolecules 1995, 28, 7901-7910, Oct. 15, 1995, (3)
PCT/US96/03302 to Matyjasewski et al., International Publication
No. W096/30421, Oct. 3, 1996, (4) M. Sawamoto et al.,
"Ruthenium-mediated Living Radical Polymerization of Methyl
Methacrylate", Macromolecules, 1996, 29, 1070.
The present inventors paid their attention to the living radical
polymerization method. As a result, it was found that the living
radical polymerization of a styrene-based polymer and an acrylic
monomer in an appropriate order using a polymerization initiator in
the presence of a transition metal and its ligand as an activating
agent makes it easy to produce a block copolymer comprising at
least two of styrene-based polymer block A and acrylic polymer
block B, i.e., A-B type or B-A type block copolymer or three-block
or higher block copolymers such as A-B-A type block copolymer.
Examples of the transition metal include Cu, Ru, Fe, Rh, V and Ni.
In general, the transition metal used is selected from the group
consisting of halides (chloride, bromide, etc.) of these metals.
The ligand is coordinated with a transition metal as a center to
form a complex. The ligandpreferably used is a bipyridine
derivative, mercaptan derivative, trifluorate derivative or the
like. Of the combinations of transition metal and its ligand,
Cu.sup.+1 -bipyridine complex is most preferable from the
standpoint of polymerization stability or polymerization rate.
The polymerization initiator preferably used is an ester-based or
styrene-based derivative containing a halogen in .alpha.-position.
In particular, a 2-bromo(or chloro)propionic acid derivative or
chloro (or bromo)-1-phenyl derivative is more preferably used.
Specific examples of these derivatives include methyl 2-bromo (or
chloro)propionate, ethyl 2-bromo (or chloro)propionate, methyl
2-bromo(or chloro)-2-methylpropionate, ethyl 2-bromo or
chloro)-2-methylpropionate and chloro(or bromo)-1-phenylethyl.
Examples of the styrene-based monomer to be used as one of the
polymerizable monomers herein include styrene,
.alpha.-methylstyrene and 2,4-dimethylstyrene. The acrylic monomer
to be used as the other one of the polymerizable monomers is an
acrylic or methacrylic acid alkyl ester represented by the general
formula (1A): CH.sub.2.dbd.CR.sup.1 COOR.sup.2 wherein R.sup.1
represents a hydrogen atom or methyl group, and R.sup.2 represents
a C.sub.2-14 alkyl group. In particular, (meth)acrylic acid alkyl
ester having a C.sub.4-12 alkyl group, such as n-butyl
(meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl
(meth)acrylate and isononyl (meth)acrylate are preferably used.
As the acrylic monomer, a modifying monomer copolymerizable with
the acrylic or methacrylic acid alkyl ester can be used in
combination with the acrylic or methacrylic acid alkyl ester. In
this case, the modifying monomer is used in an amount of 50% by
weight or less, preferably 30% by weight or less, and more
preferably 20% by weight or less, based on the total weight of the
acrylic monomer in order to obtain good pressure-sensitive adhesive
properties. Examples of the modifying monomer used include
(meth)acrylamide, maleic acid monoester, maleic acid diester,
glycidyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate,
N,N-dimethylaminopropyl (meth)acrylate, N-vinylpyrrolidone,
acrylonitrile and (meth)acryloylmorpholine.
In the living radical polymerization method, a styrene-based
monomer is first polymerized. Subsequently, an acrylic monomer is
added to continue the polymerization of monomers. Thus, an A-B type
block copolymer can be produced. During this polymerization
procedure, the acrylic monomer is added at the time when the amount
of the styrene-based monomer added exceeds at least 50% by weight,
normally 70% by weight or more, preferably 80% by weight or more,
and more preferably 90% by weight or more. On the other hand, if
the acrylic monomer is polymerized prior to the addition and
polymerization of the styrene-based monomer, a B-A type block
copolymer can be produced. Similar to the above polymerization
procedure, the styrene-based monomer is added at the time when the
amount of the acrylic monomer added exceeds at least 50% by weight,
normally 70% byweight or more, preferably 80% by weight ormore, and
more preferably 90% by weight or more.
Further, if the living radical polymerization is carried out in
amanner such thata styrene-basedmonomer is polymerized, an acrylic
monomer is added to continue polymerization of monomers, and the
styrene-based monomer is then added to continue polymerization of
monomers, an A-B-A type block copolymer can be produced. During the
successive polymerization procedure, the monomer to be subsequently
added is added at the time when the conversion of the monomer which
has been previously added exceeds at least 50% by weight, normally
60% by weight or more, preferably 80% by weight or more, and more
preferably 90% by weight or more.
Moreover, if the above three-stage polymerization is followed by
the addition of the acrylic monomer to continue the polymerization
of monomers, an A-B-A-B type block copolymer can be produced. If
this polymerization procedure is then followed by the addition of
the styrene-based monomer to continue the polymerization of
monomers, an A-B-A-B-A type block copolymer can be produced. On the
other hand, if an alternating living radical polymerization is
effected in the same manner as described above except that the
monomer to be first polymerized is changed to an acrylic monomer, a
block copolymer such as B-A-B type, B-A-B-A type and B-A-B-A-B type
block copolymers can be produced. In other words, the alternate
living radical polymerization of a styrene-based monomer and an
acrylic monomer makes it possible to produce various block
copolymers comprising at least three of a styrene-based polymer
block A and an acrylic polymer block B alternately bonded each
other.
Two or more styrene-based polymer blocks A constituting the block
copolymer comprising at least three blocks bonded each other may
not be the same but may be styrene-based polymer blocks A1, A2 and
A3 having different monomer compositions. Similarly, two or more
acrylic polymer blocks B constituting the block copolymer may be
acrylic polymer blocks B1, B2 and B3 having different monomer
compositions.
In the present invention, it is generally preferred that a
styrene-based monomer and an acrylic monomer be subjected to
alternate living radical polymerization. However, when the
styrene-based polymer blocks A (A1, A2, A3, etc.) or acrylic
polymer blocks B (B1, B2, B3, etc.) have different monomer
compositions which are definitely distinguished from each other in
properties, the order of monomers to be subjected to living radical
polymerization may be changed as necessary to produce three-block
or higher block copolymers which do not necessarily comprise a
styrene-based polymer block A and an acrylic polymer block B
alternately bonded each other, such as A1-A2-B type, B1-B2-A type,
A1-A2-B-A3 type, B1-B2-B3 type, A1-B-A2-A3 type, B1-A-B2-B3 type
and A1-B1-A2-B2 type block copolymers.
In the living radical polymerization process, the polymerization
initiator may be used in an amount of normally from 0.01 to 10 mol
%, preferably from 0.1 to 5 mol %, and more preferably from 0.1 to
2 mol %, per mole of the sum of the polymerizable monomers
containing a styrene-based monomer and an acrylic monomer (if a
monomer containing a hydroxyl group or epoxy group in its molecular
as described later is used, the sum of polymerizable monomers
containing these monomers is used). The transition metal is used in
the form of halide or the like in an amount of normally from 0.01
to 3 mols, and preferably from 0.1 to 1 mol, per mole of the
polymerization initiator. The ligand of the transition metal is
used in an amount of normally from 1 to 5 mols, and preferably from
2 to 3 mols, per mole of the transition metal which may be in the
form of halide. The use of the polymerization initiator and the
activating agent in the above defined proportion makes it possible
to provide good results in the reactivity of living radical
polymerization and the molecular weight of the resulting
polymer.
The living radical polymerization can be proceeded without solvent
or in the presence of a solvent such as butyl acetate, toluene and
xylene. If the solvent is used, it is used in a small amount such
that the solvent concentration after polymerization is 50% by
weight or less in order to prevent the drop of polymerization rate.
Even if the living radical polymerization is effected free from
solvent or in the presence of a small amount of a solvent, little
or no safety problems concerning the control over polymerization
heat can occur. Rather, reduction in the amount of solvent used
makes it possible to provide good results in economy, environmental
protection, etc. Referring to the polymerization conditions, the
living radical polymerization is carried out at a temperature of
from 70.degree. C. to 130.degree. C. for about 1 to 100 hours,
though depending the final molecular weight or polymerization
temperature, taking into account the polymerization rate or
deactivation of catalyst.
The block copolymer thus produced, if it is of A-B type, has a
structure comprising a styrene-basedi polymer block A as a starting
point having an acrylic polymer block B having a structural unit
represented by the general formula (1):
--[CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 ]-- wherein R.sup.1 represents
a hydrogen atom or methyl group, and R.sup.2 represents a
C.sub.2-14 alkyl group, bonded thereto. If it is of B-A type, the
block copolymer has a structure comprising the above acrylic
polymer block B as a starting point having the styrene-based
polymer block A bonded thereto. If it is of A-B-A type, the block
copolymer has a structure comprising a styrene-based polymer block
A as a starting point having the above acrylic polymer block B and
styrene-based polymer block A sequentially bonded thereto. If it is
of B-A-B type, the block copolymer has a structure comprising the
above acrylic polymer block B as a starting point having a
styrene-based polymer block A and an acrylic polymer block B
sequentially bonded thereto. The block copolymer comprising at
least two blocks connected to each other has a microdomain
structure as in widely used styrene-isoprene-styrene block
copolymers. It is presumed that this microdomain structure allows
the block copolymer to exhibit well-balanced pressure-sensitive
adhesive force and cohesive force when used as a pressure-sensitive
adhesive.
The block copolymer comprising at least two blocks bonded each
other comprises a styrene-based polymer block in a proportion not
exceeding 50% by weight, preferably not exceeding 40% by weight,
and more preferably 5 to 20% by weight, based on the total weight
of the copolymer if it is of A-B or B-A type, or in a proportion of
not exceeding 60% by weight, and preferably from 5 to 40% by
weight, based on the total weight of the copolymer if it is
three-block type such as A-B-A and B-A-B. If the proportion of the
styrene-based polymer block A is too large, the resulting polymer
lacks required viscoelasticity and thus is too hard for
pressure-sensitive adhesives, which is not preferable. On the other
hand, if the proportion of the styrene-based polymer block A is too
small, the resulting polymer lacks cohesive force required for
pressure-sensitive adhesives, which is also not preferable.
The present invention may optionally use, as the polymerizable
monomer, a monomer containing an epoxy group or hydroxyl group in
its molecule besides the styrene-based monomer and acrylic monomer.
In this case, the structural unit derived from these monomers is
contained in either the styrene-based polymer block A or the
acrylic polymer block B depending on the time at which these
monomers are added. Accordingly, the term "total weight of the
block copolymer" as used herein means to indicate the sum of the
weight of the styrene-based polymer block A and the acrylic polymer
block B. However, the blocks A and B each have a structural unit
derived from the above monomer containing a hydroxyl group or epoxy
group in its molecule.
In the present invention, the block copolymer comprising at least
two blocks bonded each other has a number average molecular weight
of normally from 5,000 to 500,000, and preferably from 10,000 to
200,000, from the standpoint of pressure-sensitive adhesive
properties and coatability. The term "number average molecular
weight" as used herein means to indicate value determined by GPC
(gel permeation chromatography) method in polystyrene
equivalence.
The block copolymer preferably has a proper functional group in its
polymer chain to facilitate its crosslinking at the final step. The
kind of the functional group used is appropriately selected
depending on the crosslinking method. For example, if the
crosslinking treatment is effected with a polyfunctional isocyanate
as a crosslinking agent under heating, the functional group
reactive with the crosslinking agent is preferably a hydroxyl
group. Further, in order to solve the problems concerning the
control over the reaction time, i.e., pot life, by the use of the
polyfunctional isocyanate, the functional group in the polymer
chain, if the epoxy-crosslinking treatment is effected, is
preferably an epoxy group or hydroxyl group.
The block copolymer having a hydroxyl group in its polymer chain
suitable for crosslinking can be easily produced by using a
material containing a hydroxyl group in its molecule as a
polymerization initiator and/or using a monomer containing a
hydroxyl group in its molecule as one of the polymerizable
monomers.
The use of the polymerization initiator containing a hydroxyl group
in its molecule makes it possible to introduce the hydroxyl group
into the starting end of the polymer chain. Such a polymerization
initiator used is an ester-based or styrene-based derivative
containing a halogen in a-position and having a hydroxyl group in
its molecule. Specific examples of the derivative used include
2-hydroxyethyl 2-bromo(or chloro)propionate, 4-hydroxybutyl
2-bromo(or chloro)propionate, 2-hydroxyethyl 2-bromo(or
chloro)-2-methylpropionate, and 4-hydroxybutyl 2-bromo(or
chloro)-2-methylpropionate. The polymerization initiator having a
hydroxyl group in its molecule may be used in combination with the
above polymerization initiator having no hydroxyl group in its
molecule, with the proviso that the sum of the amount of the two
polymerization initiators is as defined above.
If a monomer having a hydroxyl group in its molecule is used, the
hydroxyl group can be introduced into the polymer chain at an
arbitrary position depending on the time at which the monomer is
added. Such a monomer used is an acrylic or methacrylic acid
hydroxyalkylester represented by the general formula (2A):
CH.sub.2.dbd.CR.sup.3 COOR.sup.4 wherein R.sup.3 represents a
hydrogen atom or methyl group, and R.sup.4 represents a C.sub.2-6
alkyl group having at least one hydroxyl group. Specific examples
of the acrylic or methacrylic acid hydroxyalkylester include
2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate,
4-hydroxybutyl (meth) acrylate and 6-hydroxyhexyl (meth) acrylate.
Such a monomer is used in an amount of 10% by weight or less, and
preferably 5% by weight or less, based on the total weight of the
polymerizable monomers in order to maintain good pressure-sensitive
adhesive properties.
The combined use of a polymerization initiator having a hydroxyl
group in its molecule and a monomer having a hydroxyl group in its
molecule makes it possible to provide better results in
pressure-sensitive adhesive properties after crosslinking. In
particular, if the monomer is added in the late stage of
polymerization, i.e., at the time when the conversionof polymer
reaches 80% by weight during the formation of the final stage
polymer block (e.g., second stage for A-B or B-A type, third stage
for A-B-A or B-A-B type), the hydroxyl group of the monomer can be
introduced into the polymer chain at its terminal, in combination
with the hydroxyl group derived from the polymerization initiator
introduced into the polymer chain at its starting end. Thus, two or
more hydroxyl groups are telechelically introduced into the block
copolymer. As a result, the crosslinking reaction causes the
polymer to extend linearly, making it possible to obtain a uniform
crosslinked polymer having a small dispersion of interbridge
distance that brings about good results in the enhancement of
pressure-sensitive adhesive properties.
Examples of the block copolymer having an epoxy group or hydroxyl
group in its polymer chain suitable for epoxy crosslinking include
(a) block copolymer containing at least two epoxy groups per
molecule, (b) block copolymer containing at least one epoxy group
and at least one hydroxyl group per molecule and (c) block
copolymer containing at least two hydroxyl groups per molecule.
The block copolymer (a) preferably:contains an epoxy group
incorporated therein at or in the vicinity of the end of molecular
chain. The block copolymercanbeeasilysynthesized by using a monomer
having an epoxy group in its molecule as a monomer other than the
styrene-based or acrylic monomer with a polymerization initiator
having an epoxy group in its molecule.
If the monomer having an epoxy group in its molecule is used in the
living radical polymerization, process, the epoxy group can be
introduced into the polymer chain at an arbitrary position
depending on the time at which the monomer is added. Accordingly,
when the monomer is added in the late stage of polymerization,
i.e., at the time when the conversion of
styrene-basedmonomerandacrylicmonomer reaches 80% byweight, an
epoxy group can be introduced into the polymer chain at or in the
vicinity of the terminal thereof. If the polymerization reaction is
effected in the presence of a polymerization initiator having two
starting points per molecule, two epoxy groups are telechelically
introduced into the molecular chain of copolymer. Alternatively, by
adding the monomer separately, i.e., in the initial stage of
polymerization and the late stage of polymerization, so that an
epoxy group is introduced into the polymer chain at or in the
vicinity of starting end of the polymer chain and at or in the
vicinity of terminal of the polymer chain, the same telechelic
structure as described above can be obtained. When such a block
copolymer is epoxy-crosslinked to cure, the molecular chain of
copolymer can extend linearly, making it possible to produce a
uniform a crosslinked polymer having a small dispersion of
interbridge distance that provides good results in the enhancement
of pressure-sensitive adhesive properties.
The monomer having an epoxy group in its molecule is represented by
the general formula (3A): CH.sub.2.dbd.C(R.sup.5)COOR.sup.6 wherein
R.sup.5 represents a hydrogen atom or methyl group, and R.sup.6
represents an alkyl group containing an epoxy group. Specific
examples of the monomer include glycidyl (meth)acrylate,
methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth)
acrylate and 6-methyl-3,4-epoxycyclohexylmethyl (meth)acrylate. The
amount of such a monomer to be used is normally 40% by weight or
less, and preferably 4% by weight or less, based on the total
weight of the polymerizable monomers in order to maintain good
pressure-sensitive adhesive properties.
Further, the polymerization in the presence of the polymerization
initiator having an epoxy group in its molecule makes it possible
to introduce an epoxy group into the polymer chain at the starting
end thereof. Accordingly, if an epoxy group is introduced into the
polymer chain at the starting end thereof by using the
polymerization initiator having an epoxy group in its molecule
while introducing an epoxy group into the polymer chain at or in
the vicinity of the terminal thereof by adding the monomer having
an epoxy group in its molecule at the late stage of polymerization,
two epoxy groups are telechelically introduced into the molecular
chain of the copolymer. As a result, when the block copolymer thus
obtained is then epoxy-crosslinked to cure, the molecular chain of
the copolymer extends more linearly to produce a uniform
crosslinked polymer having a small dispersion of interbridge
distance that provides good results in the enhancement of
pressure-sensitive adhesive properties.
The polymerization initiator having an epoxy group in its molecule
used can be any ester-based or styrene-based derivative having a
halogen in .alpha.-position and an epoxy group in its molecule so
long as it does not inhibit the progress of living radical
polymerization. Specific examples of such an ester-based or
styrene-based derivative used include glycidyl 2-bromo(or
chloro)propionate, glycidyl 2-bromo(or chloro)-2-methylpropionate,
3,4-epoxycyclohexylmethyl 2-bromo(or chloro)propionate and
3,4-epoxycyclohexylmethyl 2-bromo(or
chloro)-2-methylpropionate.
The block copolymer (b) preferably comprises an epoxy group
incorporated therein at or in the vicinity of one end of the
molecular chain and a hydroxyl group incorporated therein at or in
the vicinity of the other end of the molecular chain.
Such a block copolymer can be easily synthesized by (1) using as
monomers other than the styrene-based monomer and acrylic monomer a
monomer having an epoxy group in its molecule and a monomer having
a hydroxyl group in its molecule in combination or (2) using a
polymerization initiator having a hydroxyl group in its molecule
together with the monomer having an epoxy group in its molecule or
(3) using the monomer having a hydroxyl group in its molecule
together with the polymerization initiator having an epoxy group in
its molecule.
In accordance with the method (1), a monomer having an epoxy group
in its molecule is added in the initial stage of polymerization,
and a monomer having a hydroxyl group in its molecule is then added
in the late stage of polymerization. Alternatively, the monomer
having a hydroxyl group in its molecule is added in the initial
stage of polymerization, and the monomer having an epoxy group in
its molecule is then added in the late stage of polymerization. In
this manner, an epoxy group (or hydroxyl group) can be introduced
into the polymer chain at or in the vicinity of the starting end
thereof while a hydroxyl group (or epoxy group) can be introduced
into the polymer chain at or in the vicinity of the terminal
thereof. Thus, an epoxy group and a hydroxyl group are
telechelically introduced into the molecular chain of the
copolymer. As a result, when the block copolymer thus obtained is
then crosslinked between the epoxy groups or between the epoxy
group and the hydroxyl group to cure, the molecular chain of the
copolymer extends more linearly to produce a uniform crosslinked
polymer having a small dispersion of interbridge distance that
provides good results in pressure-sensitive adhesive
properties.
In accordance with the method (2), a hydroxyl group is introduced
into the polymer chain at the starting end thereof by using a
polymerization initiator having a hydroxyl group in its molecule,
and an epoxy group is then introduced into the polymer chain at or
in the vicinity of the terminal thereof by adding a monomer having
an epoxy group in its molecule in the late stage of polymerization.
In this manner, an epoxy group and a hydroxyl group are
telechelically introduced into the molecular chain of the
copolymer. Similarly, in accordance with the method (3), an epoxy
group is introduced into the polymer chain at the starting end
thereof by using a polymerization initiator having an epoxy group
in its molecule, and a hydroxyl group is then introduced into the
polymer chain at or in the vicinity of the terminal thereof by
adding a monomer having a hydroxyl group in its molecule in the
late stage of polymerization. In this manner, an epoxy group and a
hydroxyl group are similarly telechelically introduced into the
molecular chain of the copolymer. Similarly, when the block
copolymer thus obtained is then crosslinked between the epoxy
groups or between the epoxy group and the hydroxyl group to cure,
the molecular chain of the copolymer extends more linearly to
produce a uniform crosslinked polymer having a small dispersion of
interbridge distance that provides good results in
pressure-sensitive adhesive properties.
The block copolymer (c) preferably comprises a hydroxyl group
incorporated therein at or in the vicinity of the molecular chain.
The block copolymer can be easily synthesized by using, as a
monomer other than the styrene-based monomer and acrylic monomer, a
monomer having a hydrbxyl group in its molecule, or using such a
monomer together with a polymerization initiator having a hydroxyl
group in its molecule.
A monomer having a hydroxyl group in its molecule is added in the
late stage of polymerization so that a hydroxyl group is introduced
into the polymer chain at or in the vicinity of the terminal
thereof, during which a polymerization initiator having two
starting points per molecule is used. Alternatively, the monomer is
added separately in the initial stage of polymerization and in the
late stage of polymerization so that a hydroxyl group is introduced
into the polymer chain at or in the vicinity of the starting end
thereof and at or in the vicinity of the terminal end thereof.
Alternatively, the monomer having a hydroxyl group in its molecule
is added in the late stage of polymerization so that a hydroxyl
group is introduced into the polymer chain at or in the vicinity of
the terminal thereof, during which a polymerization initiator
having a hydroxyl group in its molecule is used so that a hydroxyl
group is introduced into the polymer chain at the starting end
thereof. In this manner, a block copolymer comprising two hydroxyl
groups telechelically incorporated in its molecular chain can be
synthesized. When the block is then crosslinked with an
epoxy-crosslinking agent so that the epoxy group in the
crosslinking agent and the hydroxyl group in the copolymer are
crosslinked with each other, the molecular chain of the copolymer
extends more linearly to produce a uniform crosslinked polymer
having a small dispersion of interbridge distance that provides
good results in pressure-sensitive adhesive properties.
In the present invention, the block copolymer is crosslinked to
cause the extension of the main chain and the network formation at
the same time, thereby producing a crosslinked polymer having a
long molecular chain. The use of the crosslinked polymer as a main
component of pressure-sensitive adhesive makes it possible to
obtain an pressure-sensitive adhesive composition which remarkably
satisfies the desired pressure-sensitive adhesive properties,
particularly well-balanced pressure-sensitive adhesive peeling
force and cohesive force and excellent heat resistance. The
crosslinking method is not specifically limited. Various
conventional crosslinking methods can be employed. One of the
effective methods, if the block copolymer contains a hydroxyl group
incorporated in the polymer chain, comprises heating the block
copolymer with a polyfunctional isocyanate incorporated therein as
a crosslinking agent so that the hydroxyl group in the block
copolymer reacts with the isocyanate group as previously
described.
Examples of the polyfunctional isocyanate used include tolylene
diisocyanate, diphenylmethane diisocyanate, p-phenylene
diisocyanate, hexamethylene diisocyanate, 1,5-napthalene
diisocyanate, adducts of these diisocyanates with polyvalent
alcohols such as propanetriol, and tricyanurate derivatives
obtained by trimerizing these diisocyanates. These polyfunctional
isocyanates may be heated during crosslinking in the form of block,
particularly in the form of compound protected by ethyl
acetoacetate, methyl ethyl ketoxime, caprolactam or the like, so
that it is activated before use.
The amount of the polyfunctional isocyanate to be used depends on
the number of hydroxyl groups contained in the block copolymer. In
practice, however, the polyfunctional isocyanate is preferably used
in an amount of from 0.05 to 5 parts by weight per 100 parts by
weight of the block copolymer. If the amount of the polyfunctional
isocyanate exceeds the above defined range, the resulting
pressure-sensitive adhesive force is reduced. On the other hand, if
the amount of the polyfunctional isocyanate falls below the above
defined range, the resulting cohesive force is insufficient. The
crosslinking treatment may be effected by heating to a temperature
of from 50 to 150.degree. C. The crosslinking treatment may be
effected in the presence of a catalyst such as tin compound to
increase the crosslinking rate.
Another crosslinking method, if the block copolymer contains an
epoxy group in the polymer chain, particularly one belonging to the
block copolymers (a) to (c), comprises subjecting the block
copolymer to irradiation with ultraviolet rays in the presence of
an onium salt-based curing catalyst and optionally an epoxy-based
crosslinking agent so that it is epoxy-crosslinked. This method is
advantageous in that it requires reduced energy, can be effected at
a high efficiency and requires no heat-resistant support (i.e.,
object to which this method is applied is not limited) as compared
with the heating method using a polyfunctional isocyanate.
The epoxy-based crosslinking agent used is a compound having two or
more epoxy groups per molecule. Examples of such a compound include
ethylene glycol diglycidyl ether (hereinafter referred to as
"EGD"), glycerin diglycidyl ether, vinyl cyclohexene dioxide
represented by the general formula (El) shown later, limonene
dioxide represented by the general formula (E2) shown later,
3,4-epoxycyclohexylmethyl-3', 4'-epoxycyclohexyl carboxylate
(hereinafter referred to as "BEP') represented by the general
formula (E3) shown later, bis-(3,4-epoxycyclohexyl)adipate
represented by the general formula (E4) shown later, trifunctional
epoxy compound (hereinafter referred to as "3EP") represented by
the general formula (E5) shown later, and tetrafunctional epoxy
compound (hereinafter referred to as "4EP") represented by the
general formula (E6) shown later.
These epoxy-based crosslinking agents are not essential components
for epoxy crosslinking and thus may be or may not be used if the
block copolymer is one belonging to the block copolymers (a) and
(b) because the block copolymer has an epoxy group in its polymer
chain. On the other hand, the block copolymer (c) has no epoxy
group in its polymer chain and thus cannot be epoxy-crosslinked
without such an epoxy-based crosslinking agent. The amount of such
an epoxy-based crosslinking agent, if used, is normally 50 parts by
weight or less, and preferably 30 parts by weight or less, per 100
parts by weight of the block copolymer in order to obtain good
pressure-sensitive adhesive properties. ##STR1##
wherein a+b=1, and Z is 3,4-epoxycyclohexyl group represented by
the following general formula: ##STR2##
wherein a+b+c+d=3, and Z is 3,4-epoxycyclohexyl group represented
by the following general formula: ##STR3##
The onium salt-based curing catalyst used is preferably a diazonium
salt, sulfonium salt or iodonium salt represented by
ArN.sub.2.sup.+ Q.sup.-, Y.sub.3 S.sup.+ Q.sup.- or Y.sub.2 I.sup.+
Q.sup.-, respectively, wherein Ar represents an aryl group such as
bis (dodecylphenyl), Y represents an alkyl group or an aryl group
defined above, and Q.sup.- represents a nonbasic nucleophilic anion
such as BF.sub.4.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-,
SbF.sub.6.sup.-, SbCl.sub.6.sup.-, HSO.sub.4.sup.- and Cl.
Specific examples of the onium salt-based curing catalyst
usedincludebis(dodecylphenyl) iodoniumhexafluoroantimonate,
bis(t-butylphenyl)iodonium hexafluorophosphate,
bis(t-butylphenyl)iodonium trifluoromethanesulfonate,
triphenylsulfonium trifluoromethanesulfonate, biphenyliodonium
trifluoromethanesulfonate,
phenyl-(3-hydroxy-pentadecylphenyl)iodonium hexafluoroantimonate,
diaryliodoniumtetrakis(pentafluorophenyl)borate, and compounds
containing these components. Besides these compounds, various
mixtures containing the above components, e.g., UV-9380C, produced
by Toshiba Silicone Co., Ltd., a product containing 45% by weight
of bis (dodecylphenyl) iodonium hexafluoroantimonate, can be used.
The amount of such an onium salt-based curing catalyst to be used
is normally from 0.01 to 20 parts by weight, and preferably from
0.1 to 5 parts by weight, per 100 parts by weight of the block
copolymer. If the amount of the onium salt-based curing catalyst is
too small, the curability by crosslinking reaction is poor. On the
other hand, if the amount of the onium salt-based curing catalyst
is too large, the pressure-sensitive adhesive properties
deteriorate.
The process involving the irradiation with ultraviolet rays in the
presence of such an onium salt-based curing catalyst can be carried
out by using an appropriate ultraviolet light source such as
high-pressure mercury lamp, low-pressure mercury lamp and metal
halide lamp. The exposed dose is not specifically limited. In
practice, however, it is normally from 50 mJ to 5 J/cm.sup.2.
During this procedure, a filter or polyester sheet which cuts
ultraviolet rays at the short wave side may be used. The
irradiation temperature is not specifically limited. In practice,
however, it can normally range from room temperature to 120.degree.
C.
The pressure-sensitive adhesive composition of the present
invention may comprise a crosslinked polymer obtained by
crosslinking as described above and the block copolymer comprising
at least two of styrene-based polymer block A and acrylic polymer
block B bonded each other as a main component and optionally
various additives which are incorporated in conventional
pressure-sensitive adhesive compositions, such as tackifying
resins, fillers, antioxidants and pigments.
The pressure-sensitive adhesive sheets of the present invention are
obtained by a process which comprises applying an uncrosslinked
pressure-sensitive adhesive composition of the present invention to
one or both surfaces of a support, optionally drying the coated
material, and then subjecting the coated material to crosslinking
in the same manner as described above to form a layer of the
pressure-sensitive adhesive composition normally having a thickness
of from 10 to 100 .mu.m on each side, thereby producing a tape or
sheet form. The support used is papers, plastic-laminated papers,
cloth, plastic-laminated cloth, plastic film, metal foil, foamed
products or the like. Applying the pressure-sensitive adhesive
composition to the support can be accomplished by means of a hot
melt coater, comma roll, gravure coater, roll coater, kiss coater,
slot die coater, squeeze coater or the like.
The present invention will be further described in more detail by
reference to the following examples, but it should be understood
that the invention is not construed as being limited thereto.
Pressure-sensitive adhesive compositions comprising a crosslinked
polymer obtained by crosslinking an A-B or B-A type block copolymer
with a polyfunctional isocyanate according to Examples 1 to 30 will
be described hereinafter as compared with pressure-sensitive
adhesive compositions according to Comparative Examples 1 and
2.
The A-B type block copolymers (1) to (15) and B-A type block
copolymer (16) used in the Examples and the random copolymer (1)
used in the Comparative Examples were prepared by the following
Preparation Examples 1 to 16 and Comparative Preparation Example 1,
respectively. In those Preparation Examples, starting materials
used are mostly commercially available products. However,
2-hydroxyethyl 2-bromopropionate (hereinafter simply referred to as
"2-H2PN"), 4-hydroxybutyl 2-bromopropionate (hereinafter simply
referred to as "2-H4PN"), 2-hydroxyethyl 2-bromo-2-methylpropionate
(hereinafter simply referred to as "2-H2MPN") and 4-hydroxybutyl
2-bromo-2-methylpropionate (hereinafter simply referred to as
"2-H4MPN"), which were used as polymerization initiators having a
hydroxyl group in its molecule, were synthesized by the following
methods.
Synthesis of 2-H2PN
4.1 g (20 mmol) of dicyclohexyl carbodiimide, 5 g (81 mmol) of
anhydrous ethylene glycol and 1 ml (12 mmol) of pyridine were
charged into a reaction vessel. To the mixture were then added 14
ml of acetone and 1.5 ml (16.7 mmol) of 2-bromopropionic acid while
being cooled over ice bath to suppress an exothermic reaction.
After completion of the reaction overnight, the resulting
precipitate was removed by filtration. To the filtrate 20 ml of
ethyl acetate and 15 ml of saturated brine were added. The mixture
was then allowed to stand for a while. The resulting upper ethyl
acetate layer was washed twice with diluted hydrochloric acid and
then three times with 15 ml of saturated brine, and then dried with
anhydrous magnesium sulfate. Magnesium sulfate was removed, and
ethyl acetate was then distilled off under reduced pressure to
obtain a crude product. The crude product thus obtained was
purified through silica gel chromatography (developing solvent: 1/1
mixture of ethyl acetate and hexane) to obtain 2-H2PN as the
desired product. The yield of 2-H2PN was 1.4 g (43% by weight).
Synthesis of 2-H4PN, 2-H2MPN and 2-H4MPN
2-H4PN was synthesized in the same manner as in 2-H2PN except that
1,4-butanediol was used instead of anhydrous ethylene glycol.
2-H2MPN was synthesized in the same manner as in 2-H2PN except that
2-bromo-2-methylpropionic acid was used instead of 2-bromopropionic
acid. Further, 2-H4MPN was synthesized in the same manner as in
2-H2PN except that 1,4-butanediol was used instead of anhydrous
ethylene glycol and 2-bromo-2-methylpropionic acid was used instead
of 2-bromopropionic acid.
PREPARATION EXAMPLE 1
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was charged 45.5 g
(438 mmol) of styrene. To the content of the flask was then added
2.05 g (13.1 mmol) of 2,2'-bipyridine. The air in the reaction
system was replaced by nitrogen. In a stream of nitrogen, the
reaction mixture was heated to a temperature of 90.degree. C. with
626 mg (4.36 mmol) of copper bromide (I) added thereto in the
presence of 923 mg (4.37 mmol) of 2-H2MPN as a polymerization
initiator to initiate polymerization. The polymerization was
effected free from solvent at a temperature of 90.degree. C. for 12
hours. When the conversion (hereinafter the value obtained by
dividing the weight of the. polymer from which volatile components
have been removed by heating by the initial weight of the polymer
solution) was confirmed to have reached 80% by weight or more, 182
g (1,420 mmol) of n-butyl acrylate was added to the polymer
solution through the rubber septum. The polymer solution was
further heated for 20 hours.
When the conversion was again confirmed to have reached 80% by
weight, 1.13 g (6.56 mmol) of 6-hydroxyhexyl acrylate was added to
the polymerization system. The polymerization solution was
polymerized overnight. The polymerized product thus obtained was
diluted with ethyl acetate to a concentration of about 20% by
weight. The catalyst was removed by filtration. Finally, ethyl
acetate was distilled off. The residue was heated to a temperature
of 60.degree. C. under reduced pressure to prepare an A-B type
block copolymer (1) in the form of oily polymer.
PREPARATION EXAMPLES 2 TO 14
A-B type block copolymers (2) to (14) in the form of oily polymer
were prepared in the same manner as in Preparation Example 1 except
that the charged amount of styrene, the kind and amount of the
polymerization initiator and the kind and amount of the hydroxyl
group-containing monomer were changed as shown in Table 1. During
each of the polymerization processes, the molar amount of copper
bromide (I) to be used was the same as that of the polymerization
initiator, and the molar amount of 2,2'-bipyridine was three times
that of the polymerization initiator.
In Table 1, the abbreviation "BA" indicates n-butyl acrylate, the
abbreviation "2-BEMPN" indicates ethyl 2-bromo-2-methylpropionate,
the abbreviation "2-CEMPN" indicates ethyl
2-chloro-2-methylpropionate, the abbreviation "2-HEA" indicates
2-hydroxyethyl acrylate and the abbreviation "6-HHA" indicates
a6-hydroxyhexyl acrylate. In Table 1, the figure in the parenthesis
indicates the molar amount (mmol) of the respective starting
material component. Table 1 also contains the starting materials
used in Preparation Example 1 for reference.
TABLE 1 Hydroxyl group- Polymerization containing Styrene initiator
monomer (mmol) BA (mmol) (mmol) (mmol Preparation 45.5 g 182 g
2-H2MPN 6-HHA Example 1 (438) (1420) (4.37) (6.56) Preparation 22.8
g 182 g 2-H2MPN 6-HHA Example 2 (219) (1420) (4.37) (6.56)
Preparation 34.2 g 182 g 2-H2MPN 6-HHA Example 3 (329) (1420)
(4.37) (6.56) Preparation 45.5 g 182 g 2-H2MPN 6-HHA Example 4
(438) (1420) (10.9) (16.4) Preparation 45.5 g 182 g 2-H2MPN 6-HHA
Example 5 (438) (1420) (3.12) (4.68) Preparation 45.5 g 182 g
2-H2MPN 6-HHA Example 6 (438) (1420) (4.37) (8.74) Preparation 45.5
g 182 g 2-H2MPN 6-HHA Example 7 (438) (1420) (4.37) (4.37)
Preparation 45.5 g 182 g 2-H2MPN 2-HEA Example 8 (438) (1420)
(4.37) (6.56) Preparation 45.5 g 182 g 2-H4MPN 6-HHA Example 9
(438) (1420) (4.37) (6.56) Preparation 45.5 g 182 g 2-H2PN 6-HHA
Example 10 (438) (1420) (4.37) (6.56) Preparation 45.5 g 182 g
2-H4PN 6-HHA Example 11 (438) (1420) (4.37) (6.56) Preparation 45.5
g 182 g 2-BEMPN 6-HHA Example 12 (438) (1420) (4.37) (6.56)
Preparation 45.5 g 182 g 2-CEMPN 6-HHA Example 13 (438) (1420)
(4.37) (6.56) Preparation 45.5 g 182 g 2-H2MPN None Example 14
(438) (1420) (4.37)
The A-B type block copolymers (1) to (14) prepared in Preparation
Examples 1 to 14 were measured for number average molecular weight
[Mn], weightaverage molecularweight [Mw] and polymer dispersibility
[Mw/Mn]. The results obtained are shown in Table 2 below. For the
measurement of molecular weight, GPC method described herein was
used.
TABLE 2 Sample No. of block Mn Mw copolymer (.times.1,000)
(.times.1,000 Mw/Mn Preparation Block copolymer (1) 51.8 89.6 1.73
Example 1 Preparation Block copolymer (2) 46.7 88.3 1.89 Example 2
Preparation Block copolymer (3) 47.3 83.7 1.77 Example 3
Preparation Block copolymer (4) 21.1 43.5 2.06 Example 4
Preparation Block copolymer (5) 72.0 147.6 2.05 Example 5
Preparation Block copolymer (6) 53.2 88.8 1.67 Example 6
Preparation Block copolymer (7) 50.8 79.2 1.56 Example 7
Preparation Block copolymer (8) 52.2 97.6 1.87 Example 8
Preparation Block copolymer (9) 54.3 103.2 1.90 Example 9
Preparation Block copolymer (10) 50.5 92.4 1.83 Example 10
Preparation Block copolymer (11) 51.7 91.0 1.76 Example 11
Preparation Block copolymer (12) 52.1 81.3 1.56 Example 12
Preparation Block copolymer (13) 52.2 91.9 1.76 Example 13
Preparation Block copolymer (14) 49.9 91.3 1.83 Example 14
PREPARATION EXAMPLE 15
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was charged 45.5 g
(438 mmol) of styrene. To the content of the flask was added 2.05 g
(13.1 mmol) of 2,2'-bipyridine. The air in the reaction system was
replaced by nitrogen. In a stream of nitrogen, the reaction mixture
was heated to a temperature of 90.degree. C. with 626 mg (4.36
mmol) of copper bromide (I) added thereto in the presence of 923 mg
(4.37 mmol) of 2-H2MPN as a polymerization initiator to initiate
polymerization. The polymerization was effected free from solvent
at a temperature of 90.degree. C. for 13 hours.
When the conversion was confirmed to have reached 80% by weight or
more, a mixture of 182 g (1,420 mmol) of n-butyl acrylate and 1.13
g (6.56 mmol) of 6-hydroxyhexyl acrylate was added to the polymer
solution through the rubber septum. The polymer solution was
further heated for 25 hours. The polymerized product thus obtained
was diluted with ethyl acetate to a concentration of about 20% by
weight. The catalyst was removed by filtration. Finally, ethyl
acetate was evaporated at a temperature of 60.degree. C. under
reduced pressure to prepare an A-B type block copolymer (15) in the
form of oily polymer. The block copolymer thus obtained had a
number average molecular weight [Mn] of 52.1.times.1,000, a weight
average molecular weight [Mw] of 93.1.times.1,000 and a polymer
dispersibility [Mw/Mn] of 1.78.
PREPARATION EXAMPLE 16
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was charged 182.2 g
(1,420 mmol) of n-butyl acrylate. To the content of the flask was
added 2.05 g (13.1 mmol) of 2,2'-bipyridine. The air in the
reaction system was replaced by nitrogen. In a stream of nitrogen,
the reaction mixture was heated toatemperatureof 110.degree. C.
with 626 mg (4.36mmol) of copper bromide (I) added thereto. To the
reaction mixture was added 923 mg (4.37 mmol) of 2-H4MPN as a
polymerization initiator to initiate polymerization. The
polymerization was effected free from solvent at a temperature of
90.degree. C. for 13 hours. When the conversion was confirmed to
have reached 80% by weight or more, 45.5 g (438 mmol) of styrene
was added to the polymer solution through the rubber septum. The
polymer solution was further heated for 20 hours.
When the conversion was confirmed to have reached 90% by weight or
more, 1.13 g (6.56 mmol) of 6-hydroxyhexyl acrylate was added to
the polymer solution. The polymer solution was polymerized
overnight. The polymerized product thus obtained was then diluted
with ethyl acetate to a concentration of about 20% by weight. The
catalyst was removed by filtration. Finally, ethyl acetate was
evaporated at a temperature of 60.degree. C. under reduced pressure
to prepare an B-A type block copolymer (16) in the form of oily
polymer. The block copolymer thus obtained had a number average
molecular weight [Mn] of 50.8.times.1,000, a weight average
molecular weight [Mw] of 101.1.times.1,000 and a polymer
dispersibility [Mw/Mn] of 1.99.
COMPARATIVE PREPARATION EXAMPLE 1
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was
chargedamixtureof 45.5 g (438mmol) of styrene, 182.2 g (1,420 mmol)
of n-butyl acrylate, 0.3 g (3.84 mmol) of 2-mercaptoethanol, 1.13 g
(6.56 mmol) of 6-hydroxyhexyl acrylate and 400 ml of ethyl acetate.
To the content of the flask was added 0.5 g of azoisobutyronitrile.
The reaction mixture was heated toa temperature of 60.degree. C.
and polymerized. Finally, ethyl acetate was evaporated at a
temperature of 60.degree. C. under reduced pressure to prepare a
random copolymer (1) in the form of oily polymer. The random
copolymer thus obtained had a number average molecular weight [Mn]
of 60.8.times.1,000, a weight average molecular weight [Mw] of
122.3.times.1,000 and a polymer dispersibility [Mw/Mn] of 2.01.
EXAMPLE 1
4 g of the A-B type block copolymer (1) was diluted with 2 ml of
ethyl acetate. To the solution were added 300 mg of a 1 wt-%
toluene solution of dibutyltin laurate and 300 mg of a 10 wt-%
toluene solution of diphenylmethane diisocyanate as a crosslinking
agent to obtain an uncrosslinked pressure-sensitive adhesive
composition. Subsequently, the pressure-sensitive adhesive
composition thus obtained was applied to a polyethylene
terephthalate film having a thickness of 27 .mu.m by means of an
applicator having a gap of 200 .mu.m, and then dried at a
temperature of 120.degree. C. for 5 minutes and then at a
temperature of 50.degree. C. overnight to form an
pressure-sensitive adhesive composition layer comprising a
crosslinked polymer obtained by crosslinking the block copolymer
(1). Thus, an pressure-sensitive adhesive sheet was obtained.
EXAMPLES 2 TO 30
Various pressure-sensitive adhesive composition layers comprising a
crosslinked polymer of block copolymer were formed in the same
manner as in Example 1 except that the kind of the block copolymers
and polyfunctional isocyanates used were changed, respectively, as
shown in Tables 3 to 5 below (the amount of the two components used
were not changed). Thus, pressure-sensitive adhesive sheets were
obtained.
COMPARATIVE EXAMPLES 1 AND 2
Pressure-sensitive adhesive sheets were prepared in the same manner
as in Example 1 except that the random copolymer (1) was used
instead of the block copolymer (1) and compounds as shown in Table
5 were used as the polyfunctional isocyanate (the amount of the two
components used were not changed).
TABLE 3 Block copolymer Polyfunctional isocyanate Example 1 Block
copolymer (1) Diphenylmethane diisocyanate Example 2 " Tolylene
diisocyanate Example 3 " Hexamethylene diisocyanate Example 4 "
Trimethylolpropane derivative of diphenylmethane diisocyanate
Example 5 " Trimethylolpropane derivative of tolylene diisocyanate
Example 6 " Trimethylolpropane derivative of hexamethylene
diisocyanate Example 7 " Isocyanuric ring derivative of
hexamethylene diisocyanate Example 8 Block copolymer (2)
Diphenylmethane diisocyanate Example 9 " Trimethylolpropane
derivative of tolylene diisocyanate
TABLE 3 Block copolymer Polyfunctional isocyanate Example 1 Block
copolymer (1) Diphenylmethane diisocyanate Example 2 " Tolylene
diisocyanate Example 3 " Hexamethylene diisocyanate Example 4 "
Trimethylolpropane derivative of diphenylmethane diisocyanate
Example 5 " Trimethylolpropane derivative of tolylene diisocyanate
Example 6 " Trimethylolpropane derivative of hexamethylene
diisocyanate Example 7 " Isocyanuric ring derivative of
hexamethylene diisocyanate Example 8 Block copolymer (2)
Diphenylmethane diisocyanate Example 9 " Trimethylolpropane
derivative of tolylene diisocyanate
TABLE 5 Block copolymer or random copolymer Polyfunctional
isocyanate Example 24 Block copolymer (16) Diphenylmethane
diisocyanate Example 25 " Tolylene diisocyanate Example 26 "
Hexamethylene diisocyanate Example 27 " Trimethylolpropane
derivative of diphenylmethane diisocyanate Example 28 "
Trimethylolpropane derivative of tolylene diisocyanate Example 29 "
Trimethylolpropane derivative of hexamethylene diisocyanate Example
30 " Isocyanuric ring derivative of hexamethylene diisocyanate
Comparative Random copolymer (1) Diphenylmethane diisocyanate
Example 1 Comparative " Trimethylolpropane derivative Example 2 of
tolylene diisocyanate
The pressure-sensitive adhesive sheets of Examples 1 to 30 and
Comparative Examples 1 and 2 were measured for pressure-sensitive
adhesive force and cohesive force (creep) in the following manner.
The results obtained are shown in Tables 6 and 7 below.
Pressure-sensitive Adhesive Force
The various pressure-sensitive adhesive sheets were each cut into a
strip having a width of 20 mm and a length of 80 mm. The strip thus
prepared was press-bonded to an SUS-304 plate having a width of
40mm and a length of 100 mm by one reciprocation of a rubber roller
having a weight of 2 kg over the strip. The laminate was allowed to
standat room temperature for 30 minutes. Using a tensile testing
machine, the pressure-sensitive adhesive sheet was peeled off the
plate at an angle of 180.degree., a temperature of 25.degree. C.
and a rate of 300 mm/min to measure the force required for peeling.
The measurement was made on two samples for each pressure-sensitive
adhesive sheet. The measurement values were averaged.
Cohesive Force
The various pressure-sensitive adhesive sheets were each applied to
a bakelite plate at an area of 10 mm width and 20 mm length. The
falling distance per hour was measured at a temperature of
40.degree. C. under a load of 500 g. It is generally known that the
smaller the moving distance is, the greater is the cohesive
force.
TABLE 6 Pressure-sensitive adhesive force (g/20 mm width) Cohesive
force (mm/hr) Example 1 585 0.25 Example 2 665 0.20 Example 3 650
0.35 Example 4 530 0.14 Example 5 573 0.11 Example 6 569 0.09
Example 7 622 0.11 Example 8 582 0.44 Example 9 531 0.25 Example 10
590 0.32 Example 11 565 0.70 Example 12 458 0.15 Example 13 517
0.09 Example 14 594 0.89 Example 15 571 0.33 Example 16 573 0.26
Example 17 540 0.27 Example 18 520 0.24 Example 19 630 0.70 Example
20 685 0.95 Example 21 605 0.70 Example 22 497 0.37 Example 23 478
0.31
TABLE 7 Pressure-sensitive adhesive force (g/20 mm width) Cohesive
force (mm/hr) Example 24 627 0.45 Example 25 642 0.54 Example 26
662 0.60 Example 27 578 0.22 Example 28 563 0.30 Example 29 522
0.35 Example 30 685 0.43 Comparative 320 0.24 Example 1 Comparative
295 0.11 Example 2
As can be seen in Tables 6 and 7 above, all the pressure-sensitive
adhesive sheets of Examples 1 to 30 according to the present
invention exhibit excellent pressure-sensitive adhesive properties,
i.e., great pressure-sensitive adhesive force and cohesive force
while the pressure-sensitive adhesive sheets of Comparative
Examples 1 and 2 exhibit a poor pressure-sensitive adhesive
force.
Pressure-sensitive adhesive compositions comprising a crosslinked
polymer obtained by epoxy-crosslinking an A-B type block copolymer
according to Examples 31 to 54 will be described hereinafter as
compared with pressure-sensitive adhesive compositions according to
Comparative Examples 31 and 32.
The block copolymers (31) to (41) used in the above Examples and
the random copolymers (42) and (43) used in the foregoing
comparative examples were prepared by the following above Examples
31 to 41 and Comparative Preparation Examples 31 and 32,
respectively.
In the following Preparation Examples 31 to 41, 2-hydroxyethyl
2-bromopropionate (hereinafter simply referred to as "2-H2PN"),
2-hydroxybutyl 2-bromo-2-methylpropionate (hereinafter simply
referred to as "2-H2PN"), 3,4-epoxycyclohexylmethyl
2-bromo-2-methylpropionate (hereinafter simply referred to as
"2-MPE") and 3,4-epoxycyclohexyl 2-bromopropionate (hereinafter
simply referred to as "2-HPE"), which are polymerization
initiators, were synthesized by the following methods.
Synthesis of 2-H2PN
4.1 g (20 mmol) of dicyclohexyl carbodiimide, 5 g (81 mmol) of
anhydrous ethylene glycol and 1 ml (12 mmol) of pyridine were
charged into a reaction vessel. To the mixture was added a mixture
of 14 ml of acetone and 1.5 ml (16.7 mmol) of 2-bromopropionic acid
while being cooled over ice bath to suppress the exothermic
reaction. After completion of the reaction overnight, the resulting
precipitate was recovered by filtration. To the filtrate 20 ml of
ethyl acetate and 15 ml of saturated brine were added. The mixture
was then allowed to stand for a while. The resulting upper ethyl
acetate layer was washed twice with diluted hydrochloric acid and
then three times with 15 ml of saturated brine, and then dried over
anhydrous magnesium sulfate. Magnesium sulfate was removed. Ethyl
acetate was distilledoff under reducedpressure toobtain a crude
product. The crude product thus obtained was purified through
silica gel chromatography (developing solvent: 1/1 mixture of ethyl
acetate and hexane) to obtain 2-H2PN as the desired product. The
yield of 2-H2PN was 1 .4 g (43% by weight)
Synthesis of 2-H2MPN
2-H2MPN was synthesized in the same manner as in 2-H2PN except that
2-bromo-2-methylpropionic acid was used instead of 2-bromopropionic
acid.
Synthesis of 2-MPE
41.7 g (326 mmol) of 3,4-epoxycyclohexylmethyl alcohol, 50 ml (359
mmol) of triethylamine, 10 ml (124 mmol) of pyridine and 350 ml of
acetone were charged into a reaction vessel. To the mixture was
added a mixture of 15 ml of acetone and 40.3 ml (326 mmol) of
2-bromo-2-methylpropionic acid bromide while being cooled over ice
bath to suppress the exothermic reaction. After completion of the
reaction overnight, the resulting precipitate was recovered by
filtration. Acetone was distilled off under reduced pressure to
obtain a crude product. The crude product thus obtained was
purified through silica gel chromatography (developing solvent: 2/1
mixture of acetone and hexane) to obtain 2-MPE as the desired
product. The yield of 2-MPE was 34 g (38%)
Synthesis of 2-HPE
2-HPE was synthesized in the same manner as in 2-MPE except that
2-bromopropionic acid bromide was used instead of
2-bromo-2-methylpropionic acid bromide.
PREPARATION EXAMPLE 31
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was charged 45.5 g
(438 mmol) of styrene. To the content of the flask was then added
2.05 g (13.1 mmol) of 2,2'-bipyridine. The air in the reaction
system was replaced by nitrogen. In a stream of nitrogen, the
reaction mixture was heated to a temperature of 90.degree. C. with
626 mg (4.36 mmol) of copper bromide (I) added thereto in the
presence of 923 mg (4.37 mmol) of 2-H2MPN as a polymerization
initiator to initiate polymerization. The polymerization was
effected free from solvent at a temperature of 90.degree. C. for 12
hours. When the conversion (hereinafter the value obtained by
dividing the weight of the polymer from which volatile components
have been removed by heating by the initial weight of the polymer
solution) was confirmed to have reached 80% by weight or more, 182
g (1,420 mmol) of n-butyl acrylate was added to the polymer
solution through the rubber septum. The polymer solution was
further heated for 20 hours.
When the conversion was again confirmed to have reached 80% by
weight or more, 1.13 g (6.56 mmol) of 6-hydroxyhexyl acrylate was
added to the polymerization system. The polymerization solution was
polymerized overnight. The polymerized product thus obtained was
diluted with ethyl acetate to a concentration of about 20% by
weight. The catalyst was removed by filtration. Then, H.sup.+ -type
resin (e.g., Indion 130, 10 wt % to the block polymer) was added
into this filtrate and the mixture was stirred at 1.4.degree. C.
for 1 hour to remove bipyridine. Finally, ethyl acetate was
evaporated at a temperature of 60.degree. C. under reduced pressure
to prepare an A-B type block copolymer (31) in the form of oily
polymer.
PREPARATION EXAMPLES 32 To 41
A-B type block copolymers (32) to (41) in the form of oily polymer
were prepared in the same manner as in Preparation Example 31
except that the charged amount of styrene and n-butyl acrylate, the
kind and amount of the polymerization initiator and the kind and
amount of the hydroxyl group-or epoxy group-containing monomer were
changed as shown in Table 8. During each of the polymerization
processes, the molar amount of copper bromide (I) to be used was
the same as that of the polymerization initiator, and the molar
amount of 2,2'-bipyridine was three times that of the
polymerization initiator.
In Table 8, the abbreviation "6-HA" indicates 6-hydroxyhexyl
acrylate, the abbreviation "2-HEA" indicates 2-hydroxyethyl
acrylate and the abbreviation "3,4-ECMA" indicates
3,4-epoxycyclohexylmethyl acrylate. In Table 8, the figure in the
parenthesis indicates the molar amount (mmol) of the respective
starting material component. Table 8 also contains the starting
materials used in Preparation Example 31.
TABLE 8 Charged Kind and Kind and amount Charged amount of amount
of of hydroxyl amount of n-butyl polymerization group- or epoxy
styrene acrylate initiator group-containing (mmol) (mmol) (mmol)
monomer (mmol) Preparation 45.5 g 182 g 2-H2MPN 6-HHA Example 31
(438) (438) (4.37) (6.56) Preparation 45.5 g 182 g 2-H2MPN 6-HHA
Example 32 (438) (438) (4.37) (4.37) Preparation 22.8 g 182 g
2-H2MPN 6-HHA Example 33 (219) (438) (4.37) (6.56) Preparation 45.5
g 182 g 2-H2MPN 6-HHA Example 34 (438) (438) (8.74) (8.74)
Preparation 45.5 g 182 g 2-H2MPN 2-HHA Example 35 (438) (438)
(4.37) (6.56) Preparation 45.5 g 182 g 2-H2MPN 6-HHA Example 36
(438) (438) (4.37) (6.56) Preparation 45.5 g 182 g 2-MPE 3,4-ECMA
Example 37 (438) (438) (4.37) (6.56) Preparation 45.5 g 182 g 2-MPE
3,4-ECMA Example 38 (438) (438) (4.37) (4.37) Preparation 45.5 g
182 g 2-HPE 3,4-ECMA Example 39 (438) (438) (4.37) (6.56)
Preparation 45.5 g 182 g 2-MPE 6-HHA Example 40 (438) (438) (4.37)
(6.56) Preparation 45.5 g 182 g 2-H2MPN 3,4-ECMA Example 41 (438)
(438) (4.37) (6.56)
The A-B type block copolymers (31) to (41) prepared in Preparation
Examples 31 to 41 were measured for number average molecular weight
[Mn], weight average molecular weight [Mw] and polymer
dispersibility [Mw/Mn]. The results obtained are shown in Table 9
below. For the measurement of molecular weight, GPC method
described herein was used.
TABLE 9 Sample No. of block Mn Mw copolymer (.times.1,000)
(.times.1,000) Mw/Mn Preparation Block copolymer (31) 51.8 89.6
1.73 Example 31 Preparation Block copolymer (32) 53.2 90.2 1.70
Example 32 Preparation Block copolymer (33) 40.8 78.6 1.93 Example
33 Preparation Block copolymer (34) 25.2 51.3 2.04 Example 34
Preparation Block copolymer (35) 50.5 86.2 1.71 Example 35
Preparation Block copolymer (36) 49.8 79.9 1.60 Example 36
Preparation Block copolymer (37) 48.6 80.1 1.65 Example 37
Preparation Block copolymer (38) 50.6 90.9 1.80 Example 38
Preparation Block copolymer (39) 53.2 89.6 1.68 Example 39
Preparation Block copolymer (40) 47.6 78.3 1.64 Example 40
Preparation Block copolymer (41) 51.3 92.8 1.81 Example 41
COMPARATIVE PREPARATION EXAMPLE 31
Into the same four-necked flask as used in Preparation Example 31
were charged 45.5 g (438 mmo1) of styrene, 182 g (1,420 mmol) of
n-butyl acrylate, 1.13 g (6.56 mmol) of 6-hydroxyhexyl acrylate,
0.3 g (3.84 mmol) of 2-mercaptoethanol and 400 ml of ethyl acetate.
To the mixture was added 0.5 g of azoisobutyrolintrile. The
reaction mixture was heated to a temperature of 60.degree. C. for 5
hours to conduct polymerization. After completion of the
polymerization, ethyl acetate was evaporated at a temperature of
60.degree. C. under reduced pressure to obtain an oily random
copolymer (42). The random copolymer (42) thus obtained had a
number average molecular weight [Mn] of 60.8.times.1,000, a weight
average molecular weight [Mw] of 122.3.times.1,000 and a polymer
dispersibility [Mw/Mn] of 2.01.
COMPARATIVE PREPARATION EXAMPLE 32
Into the same four-necked flask as used in Preparation Example 1
were charged 45.5 g (438 mmol) of styrene, 182 g (1,420 mmol) of
n-butyl acrylate, 1.19 g (6.56 mmol) of 3,4-epoxycyclohexylmethyl
acrylate, 0.3 g (1.48 mmol) of dodecanethiol and 400 ml of ethyl
acetate. To the mixture was then added 0.5 g of
azoisobutyrolintrile. The reaction mixture was heated to a
temperature of 60.degree. C. for 5 hours to conduct polymerization.
After completion of the polymerization, ethyl acetate was
evaporated at a temperature of 60.degree. C. under reduced pressure
to obtain an oily random copolymer (43). The random copolymer (43)
thus obtained had a number average molecular weight [Mn] of
59.4.times.1,000, a weight average molecular weight [Mw] of
136.times.1000and a polymer dispersibility [Mw/Mn] of 2.29.
EXAMPLE 31
4 g of the A-B type block copolymer (31) was diluted with 4 ml of
ethyl acetate. To the solution were added 120 mg of "UV-9380C"
[iodonium salt-based curing catalyst produced by Toshiba Silicone
Co., Ltd.; a chemical product containing 45% by weight of
bis(dodecylphenyl)iodoniumhexafluoroantimonate] and 0.1 g of BEP
(3,4-epoxycyclohexylmethyl-3',4'-epoxycylcohexyl carboxylate) as a
crosslinking agent. The mixture was uniformly stirred to prepare a
pressure-sensitive adhesive composition solution before
epoxy-crosslinking. The pressure-sensitive adhesive composition
solution thus obtained was applied to a polyethylene terephthalate
film (hereinafter referred to as "PET film") having a thickness of
27 .mu.m by means of an applicator having a gap of 100 .mu.m, dried
at a temperature of 120.degree. C. for 5 minutes, and then
irradiated with ultraviolet rays from a high pressure mercury lamp
at a dose of 1.3 J at room temperature to epoxy-crosslink, to
thereby form an pressure-sensitive adhesive composition layer
comprising a crosslinked polymer obtained by crosslinking the block
copolymer. Thus, an pressure-sensitive adhesive sheet was
obtained.
EXAMPLES 32 to 54
23 kinds of pressure-sensitive adhesive composition solutions
before epoxy-crosslinking were prepared in the same manner as in
Example 31 except that the kind of the A-B block copolymers (the
amount used was not changed) and the kind and amount of the onium
salt-based curing catalysts (photo-acid generator) were changed as
shown in Tables 10 and 11 and the epoxy-based crosslinking agent to
be used was changed in its kind and amount as shown in Tables 10
and 11 or was not used. Further, pressure-sensitive adhesive layers
containing a crosslinked polymer of the various block copolymers
were formed on the PET film from these composition solutions in the
same manner as in Example 31 except that the exposed dose of
ultraviolet rays was determined as shown in Tables 10 and 11. Thus,
pressure-sensitive adhesive sheets were prepared.
Table 10 also contains the kind of the A-B type block copolymer
used in Example 31 and the kind and amount of the onium salt-based
curing catalyst used in Example 31 for reference. In Tables 10 and
11, the abbreviations "BBI-102", "BBI-105", "TPS-105", "DPI-105"
and "CD1012" as onium-based curing catalysts indicate
bis(t-butylphenyl)iodoniumhexafluoro phosphate,
bis(t-butylphenyl)iodoniumtrifluoromethane sulfonate,
triphenylsulfonium trifluoromethane sulfonate, biphenyliodonium
trifluoromethane sulfonate and
phenyl(3-hydroxy-pentadecylphenyl)iodoniumhexafluoroantimonate,
respectively. As crosslinking agents (epoxy compounds), the
abbreviations "BEP", "EGD", "3EP" and "4EP" are as defined
hereinabove.
COMPARATIVE EXAMPLES 31 AND 32
Two kinds of pressure-sensitive adhesive composition solutions
before epoxy-crosslinking were prepared in the same manner as in
Example 31 except that the random copolymers (42) and (43) were
used instead of the block copolymer (the amount used was not
changed), respectively, and the kind and amount of the onium
salt-based curing catalyst (photo-acid generator) and epoxy
crosslinking agent were changed as set forth in Table 11.
Pressure-sensitive adhesive layers containing a crosslinked polymer
of the random copolymers were then formed on PET film from these
solutions in the same manner as in Example 31. Thus,
pressure-sensitive adhesive sheets were prepared.
TABLE 10 Dose of Onium salt- Cross- ultra- based curing linking
violet Block copolymer catalyst (g) agent (g) rays (J) Example 31
Block copolymer (31) UV-9380C BEP 1.3 (0.12) (0.1) Example 32 "
UV-9380C BEP 0.26 (0.12) (0.1) Example 33 " UV-9380C BEP 2.6 (0.12)
(0.1) Example 34 " BBI-102 BEP 1.3 (0.06) (0.1) Example 35 "
BBI-102 BEP " (0.12) (0.1) Example 36 " BBI-102 BEP " (0.06) (0.2)
Example 37 " BBI-102 EGD " (0.06) (0.1) Example 38 " BBI-102 3EP "
(0.06) (0.1) Example 39 " BBI-102 4EP " (0.06) (0.1) Example 40 "
BBI-105 BEP " (0.06) (0.1) Example 41 " TPS-105 BEP " (0.06) (0.1)
Example 42 " DPI-105 BEP " (0.06) (0.1) Example 43 " CD1012 BEP "
(0.06) (0.1) Example 44 Block copolymer (32) BBI-102 BEP (0.06)
(0.1) Example 45 Block copolymer (33) BBI-102 BEP (0.06) (0.1)
Example 46 Block copolymer (34) BBI-102 BEP (0.06) (0.1) Example 47
Block copolymer (35) BBI-102 BEP (0.06) (0.1) Example 48 Block
copolymer (36) BBI-102 BEP (0.06) (0.1)
TABLE 10 Dose of Onium salt- Cross- ultra- based curing linking
violet Block copolymer catalyst (g) agent (g) rays (J) Example 31
Block copolymer (31) UV-9380C BEP 1.3 (0.12) (0.1) Example 32 "
UV-9380C BEP 0.26 (0.12) (0.1) Example 33 " UV-9380C BEP 2.6 (0.12)
(0.1) Example 34 " BBI-102 BEP 1.3 (0.06) (0.1) Example 35 "
BBI-102 BEP " (0.12) (0.1) Example 36 " BBI-102 BEP " (0.06) (0.2)
Example 37 " BBI-102 EGD " (0.06) (0.1) Example 38 " BBI-102 3EP "
(0.06) (0.1) Example 39 " BBI-102 4EP " (0.06) (0.1) Example 40 "
BBI-105 BEP " (0.06) (0.1) Example 41 " TPS-105 BEP " (0.06) (0.1)
Example 42 " DPI-105 BEP " (0.06) (0.1) Example 43 " CD1012 BEP "
(0.06) (0.1) Example 44 Block copolymer (32) BBI-102 BEP (0.06)
(0.1) Example 45 Block copolymer (33) BBI-102 BEP (0.06) (0.1)
Example 46 Block copolymer (34) BBI-102 BEP (0.06) (0.1) Example 47
Block copolymer (35) BBI-102 BEP (0.06) (0.1) Example 48 Block
copolymer (36) BBI-102 BEP (0.06) (0.1)
The pressure-sensitive adhesive sheets of Examples 31 to 54 and
Comparative Examples 31 and 32 were measured for pressure-sensitive
adhesive force and holding force (cohesive force) in the following
manner. The results obtained are shown in Tables 12 and 13
below.
Measurement of Pressure-sensitive Adhesive Force
The various pressure-sensitive adhesive sheets were each cut into a
strip having a width of 20 mm and a length of 80 mm. The strip thus
prepared was press-bonded to an SUS-304 plate having a width of 40
mm and a length of 100 mm by one reciprocation of a rubber roller
having a weight of 2 kg once over the strip. The laminate was
allowed to stand at room temperature for 30 minutes. Using a
tensile testing machine, the pressure-sensitive adhesive sheet was
peeled off the plate at an angle of 180.degree., a temperature of
25.degree. C. and a rate of 300 mm/min to measure the force
required for peeling. The measurement was made on two samples for
each pressure-sensitive adhesive sheet. The measurement values were
averaged.
Measurement of Holding Force
The various pressure-sensitive adhesive sheets were each applied to
a bakelite plate at an area of 10 mm width and 20 mm length. The
falling distance per hour was then measured at a temperature of
40.degree. C. under a load of 500 g. It is generally known that the
smaller the falling distance is, the greater is the cohesive
force.
TABLE 12 Pressure-sensitive adhesive force (g/20 mm width) Holding
force (mm/hr) Example 31 572 0.18 Example 32 373 0.39 Example 33
682 0.19 Example 34 579 0.19 Example 35 552 0.20 Example 36 568
0.21 Example 37 397 0.38 Example 38 406 0.18 Example 39 478 0.11
Example 40 370 0.17 Example 41 405 0.19 Example 42 466 0.22 Example
43 555 0.15 Example 44 586 0.22 Example 45 465 0.32 Example 46 459
0.15 Example 47 520 0.20 Example 48 494 0.27
TABLE 12 Pressure-sensitive adhesive force (g/20 mm width) Holding
force (mm/hr) Example 31 572 0.18 Example 32 373 0.39 Example 33
682 0.19 Example 34 579 0.19 Example 35 552 0.20 Example 36 568
0.21 Example 37 397 0.38 Example 38 406 0.18 Example 39 478 0.11
Example 40 370 0.17 Example 41 405 0.19 Example 42 466 0.22 Example
43 555 0.15 Example 44 586 0.22 Example 45 465 0.32 Example 46 459
0.15 Example 47 520 0.20 Example 48 494 0.27
As can be seen from Tables 12 and 13 above, all the
pressure-sensitive adhesive sheets of Examples 31 to 54 comprising
as a main component a crosslink ed polymer obtained by
epoxy-crosslinking block copolymers obtained by living radical
polymerization exhibit excellent pressure-sensitive adhesive
properties, i.e., great pressure-sensitive adhesive force and
cohesive force. Further, the various pressure-sensitive adhesive
sheets according to Examples 31 to 54 exhibit an excellent light
resistance based on the acrylic polymer block B and an excellent
heat resistance based on the epoxy crosslinking treatment.
Moreover, since these pressure-sensitive adhesives are prepared
free from a large amount of a solvent or water, no problems occur
in economy, working atmosphere, safety, etc. as well as in pot
life.
On the other hand, the pressure-sensitive adhesive sheets according
to Comparative Examples 31 and 32 comprising as a main component a
crosslinked polymer obtained by epoxy-crosslinking an ordinary
random copolymer are poor in the pressure-sensitive adhesive
properties. In particular, these pressure-sensitive adhesive sheets
exhibit a definitely small pressure-sensitive adhesive force.
Pressure-sensitive adhesive compositions comprising a crosslinked
polymer obtained by crosslinking an A-B-A type block copolymer
according to Examples 61 to 93 will be described hereinafter as
compared with pressure-sensitive adhesive compositions according to
Comparative Examples 61 and 63.
The A-B-A type block copolymers (61) to (67) used in the above
Examples and the random copolymer (68) used in the above
Comparative Examples were prepared by the following Preparation
Examples 61 to 67 and Comparative Preparation Example 1,
respectively. In these Preparation Examples, the starting materials
used are mostly commercially available products. However,
2-hydroxyethyl 2-bromo-2-methylpropionate (hereinafter simply
referred to as "2-H2MPN"), which was used as a polymerization
initiator having a hydroxyl group in its molecule, was synthesized
by the following method.
Synthesis of 2-H2MPN
Excess amounts of ethylene glycol (44 ml (788 mmol)), triethylamine
(100 ml (717 mmol)) and pyridine (20 ml (200 mmol)) were charged
into a reaction vessel. To the mixture were added 800 ml of acetone
and 150 g (652 mmol) of 2-bromoisobutylyl bromide while being
cooled over ice bath to suppress the exothermic reaction. After 16
hours of reaction, the resulting precipitate was recovered by
filtration. To the precipitate thus recovered were added 1 liter of
ethyl acetate and 500 ml of saturated brine. The mixture was
thoroughly shaken. The mixture was allowed to stand for a while.
The resulting upper ethyl acetate layer was washed twice with
diluted hydrochloric acid and then three times with 500 ml of
saturated brine, and then dried over anhydrous magnesium sulfate.
Magnesium sulfate was removed. Ethyl acetate was distilled off
under reduced pressure to obtain a crude product. The crude product
thus obtained was purified by distillation method (87 to 90.degree.
C./0.25 mmHg) to obtain 2-H2MPN as the desired product. The yield
of 2-H2MPN was 88 g (64% by weight).
PREPARATION EXAMPLE 61
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was charged 14.2 g
(137 mmol) of styrene. To the content of the flask was added 1.3 g
(8.3 mmol) of 2,2'-bipyridine. The air in the reaction system was
replaced by nitrogen. In a stream of nitrogen, the reaction mixture
was heated to a temperature of 90.degree. C. with 410 mg (2.84
mmol) of copper bromide (I) added thereto in the presence of 600 mg
(2.84 mmol) of 2-H2MPN as a polymerization initiator to initiate
polymerization. The polymerization was effected free from solvent
at a temperature of 90.degree. C. for 12 hours. When the conversion
(hereinafter the value obtained by dividing the weight of the
polymer from which volatile components have been removed by heating
by the initial weight of the polymer solution) was confirmed to
have reached 80% by weight or more, 85 g (662 mmol) of n-butyl
acrylate was added to the polymer solution through the rubber
septum. The polymer solution was further heated to a temperature of
110.degree. C. for 20 hours. When the conversion was again
confirmed to have reached 80% by weight or more, 14.2 g (137 mmol)
of styrene was added to the polymerization system through the
rubber septum. The polymerization solution was heated to a
temperature of 90.degree. C. for 20 hours. The polymerized product
thus obtained was diluted with ethyl acetate to a concentration of
about 20% by weight. The catalyst was removed by filtration. Then,
H.sup.+ -type resin (e.g., Indion 130, 10 wt % to the block
polymer) was added into this filtrate and the mixture was stirred
at 1.4.degree. C. for 1 hour to remove bipyridine. Finally, ethyl
acetate was evaporated at a temperature of 50.degree. C. under
reduced pressure to prepare an A-B-A type block copolymer (61) in
the form of oily polymer.
PREPARATION EXAMPLE 62
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was charged 14.2 g
(137 mmol) of styrene. To the content of the flask was added 1.3 g
(8.3 mmol) of 2,2'-bipyridine. The air in the reaction system was
replaced by nitrogen. In a stream of nitrogen, the reaction mixture
was heated to a temperature of 90.degree. C. with 410 mg (2.84
mmol) of copper bromide (I) added thereto in the presence of 600 mg
(2.84 mmol) of 2-H2MPN as a polymerization initiator to initiate
polymerization. The polymerization was effected free from solvent
at a temperature of 90.degree. C. for 12 hours. When the conversion
was confirmed to have reached 80% by weight or more, 85 g (662
mmol) of n-butyl acrylate was added to the polymer solution through
the rubber septum. The polymer solution was further heated to a
temperature of 110.degree. C. for 20 hours. When the conversion was
again confirmed to have reached 80% by weight or more, 7:40 mg
(4.28 mmol) of 6-hydroxyhexyl acrylate was added to the
polymerization system. The polymerization solution was polymerized
for 16 hours. Finally, to the polymerization solution was added
14.2 g (137 mmol) of styrene through the rubber septum. The
polymerization solution was heated to a temperature of 90.degree.
C. for 20 hours. The polymerized product thus obtained was diluted
with ethyl acetate to a concentration of about 20% by weight. The
catalyst was removed by filtration. Then, H.sup.+ -type resin
(e.g., Indion 130, 10 wt % to the block polymer) was added into
this filtrate and the mixture was stirred at 1.4.degree. C. for 1
hour to remove bipyridine. Finally, ethyl acetate was evaporated at
a temperature of 50.degree. C. under reduced pressure to prepare an
A-B-A type block copolymer (62) in the form of oily polymer.
PREPARATION EXAMPLES 63 TO 66
A-B-A type block copolymers (63) to (66) in the form of oily
polymer were prepared in the same manner as in Preparation Example
62 except that the amount of styrene charged in the first stage,
the kind and amount of the acrylic monomer charged in the second
stage and the amount of styrene charged in the third stage
initiator were changed as shown in Table 14 although the charged
amount of 2-H2MPN as a polymerization initiator and the charged
amount of 6-hydroxyhexyl acrylate as an acrylic monomer having a
hydroxyl group in its molecule were not changed. During each of the
polymerization processes, the molar amount of copper bromide (I) to
be used was the same as that of the polymerization initiator, and
the molar amount of 2,2'-bipyridine was three times that of the
polymerization initiator. Table 14 also contains the amount of the
monomers used in the first to third stages in Preparation Example
62 for reference.
In Table 14, the abbreviation "BA" indicates n-butyl acrylate, the
abbreviation "2-HEA" indicates 2-hydroxyethyl acrylate, and the
abbreviation "HA" indicates hexyl acrylate. In Table 14, the figure
in the parenthesis indicates the molar amount (mmol) of the
respective starting material component.
TABLE 14 Kind and amount of acrylic Styrene monomer Styrene charged
in 1st charged in 2nd charged in 3rd stage (mmol) stage (mmol)
stage (mmol) Preparation 14.2 g (137) BA 85 g (662) 14.2 g (137)
Example 62 Preparation 28.4 g (273) BA 85 g (662) 28.4 g (273)
Example 63 Preparation 7.1 g (69) 2EHA 85 g (461) 7.1 (69) Example
64 Preparation 7.1 g (69) HA 85 g (544) 7.1 g (69) Example 65
Preparation 14.2 g (137) BA 43 g (335) 14.2 g (137) Example 66 2EHA
43 g (233)
PREPARATION EXAMPLE 67
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum was charged 14.2 g
(137 mmol) of styrene. To the content of the flask was added 1.3 g
(8.3 mmol) of 2,2'-bipyridine. The air in the reaction system was
replaced by nitrogen. In a stream of nitrogen, the reaction mixture
was heated to a temperature of 90.degree. C. with 410 mg (2.84
mmol) of copper bromide (I) added thereto in the presence of 600 mg
(2.84 mmol) of 2-H2MPN as a polymerization initiator to initiate
polymerization. The polymerization was effected free from solvent
at a temperature of 90.degree. C. for 12 hours. When the conversion
was confirmed to have reached 80% by weight or more, 85 g (662
mmol) of n-butyl acrylate was added to the polymer solution through
the rubber septum. The polymer solution was further heated to a
temperature of 110.degree. C. for 20 hours. When the conversion was
again confirmed to have reached 80% by weight or more, 14.2 mg (137
mmol) of styrene was added to the polymerization solution through
the rubber septum. The polymerization solution was heated to a
temperature of 90.degree. C. for 20 hours. Finally, 740 mg (4.28
mmol) of 6-hydroxyhexyl acrylate was added to the polymerization
system. The polymerization solution was polymerized for 16 hours.
The polymerized product thus obtained was diluted with ethyl
acetate to a concentration of about 20% by weight. The catalyst was
removed by filtration. Then, H.sup.+ -type resin (e.g., Indion 130,
10 wt % to the block polymer) was added into this filtrate and the
mixture was stirred at 1.4.degree. C. for 1 hour to remove
bipyridine. Finally, ethyl acetate was evaporated at a temperature
of 50.degree. C. under reduced pressure to prepare an A-B-A type
block copolymer (67) in the form of oily polymer.
The A-B-A type block copolymers (61) to (67) prepared in
Preparation Examples 61 to 67 were measured for number average
molecular weight [Mn], weight average molecular weight [Mw] and
polymer dispersibility [Mw/Mn]. The results obtained are shown in
Table 15 below. For the measurement of molecular weight, GPC method
described herein was used.
TABLE 15 Sample No. of block Mn (x Mw (x copolymer 1,000) 1,000)
Mw/Mn Preparation Block copolymer (61) 42.0 79.2 1.89 Example 61
Preparation Block copolymer (62) 44.1 78.6 1.78 Example 62
Preparation Block copolymer (63) 52.7 104.0 1.97 Example 63
Preparation Block copolymer (64) 49.2 99.1 2.01 Example 64
Preparation Block copolymer (65) 39.6 78.6 1.98 Example 65
Preparation Block copolymer (66) 47.8 90.1 1.88 Example 66
Preparation Block copolymer (67) 42.1 83.1 1.97 Example 67
COMPARATIVE PREPARATION EXAMPLE 61
Into a four-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, a condenser and a rubber septum were charged 45.5 g
(438 mmol) of styren 182 g (1,420 mmol) of n-butyl acrylate, 0.3 g
(3.84 mmol) of 2-mercaptoethanol, 1.13 g (6.56 mmol) of
6-hydroxyhexyl acrylate and400 ml of ethyl acetate. To the mixture
was added 0.5 gof azoisobutyrolintrile. The reaction mixture was
heated to a temperature of 60.degree. C. for 5 hours to conduct
polymerization. Then, H.sup.+ -type resin (e.g., Indion 130, 10 wt
% to the block polymer) was added into this filtrate and the
mixture was stirredat 1.4.degree. C. for 1 hour to remove
bipyridine. Finally, ethyl acetate was evaporated at a temperature
of 60.degree. C. under reduced pressure to obtain an oily random
copolymer (68). The random copolymer (68) thus obtained had a
number average molecular weight [Mn] of 60.8.times.1,000, a weight
average molecular weight [Mw] of 122.3.times.1,000 and a polymer
dispersibility [Mw/Mn] of 2.01.
EXAMPLE 61
4 g of the A-B-A type block copolymer (61) was diluted with 2 ml of
ethyl acetate. To the solution were added 300 mg of a 1 wt %
toluene solution of dibutyltin laurate and 300 mg of a 10 wt %
toluene solution of diphenylmethane diisocyanate as a crosslinking
agent to obtain a pressure-sensitive adhesive composition before
crosslinking. Subsequently, the pressure-sensitive adhesive
composition thus obtained was applied to a polyethylene
terephthalate film (hereinafter referred to as "PET film") having a
thickness of 25 .mu.m by means of an applicator having a gap of 200
.mu.m, and dried at a temperature of 120.degree. C. for 5 minutes
and then at a temperature of 50.degree. C. for 16 hours to form a
pressure-sensitive adhesive composition layer comprising a
crosslinked polymer obtained by crosslinking the block copolymer
(61) Thus, an pressure-sensitive adhesive sheet was obtained.
EXAMPLES 62 TO 74
Various pressure-sensitive adhesive composition layers comprising a
crosslinked polymer of block copolymer were formed on PET film in
the same manner as in Example 61 except that the kind of the block
copolymers and polyfunctional isocyanates used were changed,
respectively, as shown in Tables 16 to 17 below (the amount of the
two components used were not changed). Thus, pressure-sensitive
adhesive sheets were obtained. Table 16 also contains the kind of
block copolymer and polyfunctional isocyanate used in Example 61
for reference.
COMPARATIVE EXAMPLES 61 AND 62
Pressure-sensitive adhesive composition layers containing a
crosslinked polymer of the random copolymer were each formedon PET
film in the samemanner as in Example 61 except that the random
copolymer (68) was used instead of the block copolymer (61) and the
compound as shown in Table 17 (the amount of the two components
used were not changed) was used as the polyfunctional isocyanate.
Thus, pressure-sensitive adhesive sheets were prepared.
TABLE 16 Block copolymer Polyfunctional isocyanate Example 61 Block
copolymer (61) Diphenylmethane diisocyanate Example 62 Block
copolymer (61) Trimethylolpropane derivative of tolylene
diisocyanate Example 63 Block copolymer (62) Diphenylmethane
diisocyanate Example 64 Block copolymer (62) Tolylene diisocyanate
Example 65 Block copolymer (62) Hexamethylene diisocyanate Example
67 Block copolymer (62) Trimethylolpropane derivative of
diphenylmethane diisocyanate Example 67 Block copolymer (62)
Trimethylolpropane derivative of tolylene diisocyanate Example 68
Block copolymer (62) Trimethylolpropane derivative of hexamethylene
diisocyanate Example 69 Block copolymer (62) Isocyanuric ring
derivative of hexamethylene diisocyanate
TABLE 17 Block copolymer or random copolymer Polyfunctional
isocyanate Example 70 Block copolymer (63) Isocyanuric ring
derivative of hexamethylene diisocyanate Example 71 Block copolymer
(64) Isocyanuric ring derivative of hexamethylene diisocyanate
Example 72 Block copolymer (65) Isocyanuric ring derivative of
hexamethylene diisocyanate Example 73 Block copolymer (66)
Isocyanuric ring derivative of hexamethylene diisocyanate Example
74 Block copolymer (67) Isocyanuric ring derivative of
hexamethylene diisocyanate Comparative Random copolymer (68)
Diphenylmethane diisocyanate Example 1 Comparative Random copolymer
(68) Trimethylolpropane derivative Example 2 of tolylene
diisocyanate
EXAMPLE 75
4 g of the A-B-A type block copolymer (61) was diluted with 4 ml of
ethyl acetate. To the solution were added 120 mg of "UV-9380C"
[iodonium salt-based curing catalyst produced by Toshiba Silicone
Co., Ltd.; a chemical product containing 45% by weight of bis
(dodecylphenyl) iodoniumhexafluoroantimonate] and 0.1 g of BEP
(3,4-epoxycycohexylmethyl-3', 4'-epoxycylcohexyl carboxylate) as a
crosslinking agent. The mixture was uniformly stirred to prepare an
uncrosslinked pressure-sensitive adhesive composition solution. The
pressure-sensitive adhesive composition solution thus obtained was
applied to PET film having a thickness of 25 .mu.m by means of an
applicator having a gap of 100 .mu.m, dried at a temperature of
120.degree. C. for 5 minutes, and then irradiated with ultraviolet
rays from a high pressure mercury lamp at an exposed dose of 1.3 J
at room temperature to crosslink the same to thereby form an
pressure-sensitive adhesive composition layer comprising a
crosslinked polymer obtained by crosslinking the foregoing block
copolymer (61). Thus, a pressure-sensitive adhesive sheet was
obtained.
EXAMPLES 76 TO 93
Uncrosslinked pressure-sensitive adhesive composition solutions
were prepared in the same manner as in Example 75 except that the
kind of the block copolymers (the amount used was not changed) and
the kind and amount of the onium salt-based curing catalysts
(photo-acid generator) and the epoxy-based crosslinking agents to
be used were changed as shown in Table 18. Further,
pressure-sensitive adhesive layers containing a crosslinked polymer
of the various block copolymers were formed on the PET film from
these composition solutions in the same manner as in Example 75
except that the dose.of ultraviolet rays was determined as shown in
Table 18. Thus, pressure-sensitive adhesive sheets were prepared.
Table 18 also contains the kind of the block copolymer used in
Example 75 and the kind and amount of the onium salt-based curing
catalyst used in Example 75 for reference.
In Table 18, the abbreviations "BBI-102", "BBI-105", "TPS-105",
"DPI-105" and "CD1012" as onium-based curing catalysts indicate
bis(t-butylphenyl)iodoniumhexafluoro phosphate,
bis(t-butylphenyl)iodoniumtrifluoromethane sulfonate,
triphenylsulfonium trifluoromethane sulfonate, biphenyliodonium
trifluoromethane sulfonate and phenyl
(3-hydroxy-pentadecylphenyl)iodoniumhexafluoroantimonate,
respectively. The abbreviations "BEP", "EGD", "3EP" and "4EP"as
epoxy-based crosslinking agents are the same as defined
hereinabove.
COMPARATIVE EXAMPLE 63
Uncrosslinked pressure-sensitive adhesive composition solutions
were prepared in the same manner as in Example 75 except that the
random copolymer (68) was used instead of the block copolymer (the
amount used was not changed) and the kind and amount of the onium
salt-based curing catalysts (photo-acid generator) and epoxy-based
crosslinking agents to be used were changed as shown in Table 18.
Further, pressure-sensitive adhesive composition layers containing
a crosslinked polymer of the random copolymers were each formed
from these composition solutions on PET film in the same manner as
in Example 75 to prepare pressure-sensitive adhesive sheets.
TABLE 18 Onium salt-based Dose of curing Crosslinking ultraviolet
Block catalyst agent rays copolymer (g) (g) (J) Example 75 Block
UV-9380C BEP (0.1) 1.3 copolymer (0.12) (61) Example 76 Block
BBI-102 BEP (0.1) 1.3 copolymer (0.06) (61) Example 77 Block UV-102
BEP (0.1) 0.26 copolymer (0.12) (62) Example 78 Block UV-102 BEP
(0.1) 2.6 copolymer (0.12) (62) Example 79 Block BBI-102 BEP (0.1)
1.3 copolymer (0.06) (62) Example 80 Block BBI-102 BEP (0.2) 1.3
copolymer (0.12) (62) Example 81 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (62) Example 82 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (62) Example 83 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (62) Example 84 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (62) Example 85 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (62) Example 86 Block TPS-105 BEP (0.1) 1.3
copolymer (0.06) (62) Example 87 Block CD1012 BEP (0.1) 1.3
copolymer (0.06) (62) Example 68 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (62) Example 89 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (63) Example 90 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (64) Example 91 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (65) Example 92 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (66) Example 93 Block BBI-102 BEP (0.1) 1.3
copolymer (0.06) (67) Comparative Random BBI-102 BEP (0.1) 1.3
Example 63 copolymer (0.06) (68)
The pressure-sensitive adhesive sheets of Examples 61 to 93 and
Comparative Examples 61 and 63 were measured for pressure-sensitive
adhesive force and cohesive force (creep) in the following manner.
The results obtained are shown in Tables 19 and 20 below.
Pressure-sensitive Adhesive Force
The various pressure-sensitive adhesive sheets were each cut into a
strip having a width of 20 mm and a length of 80 mm. The strip thus
prepared was press-bonded to an SUS-304 plate having a width of
40mm and a length of 100 mm by one reciprocation of a rubber roller
having a weight of 2 kg once over the strip. The laminate was then
allowed to stand at room temperature for 30 minutes. Using a
tensile testing machine, the pressure-sensitive adhesive sheet was
peeled off the plate at an angle of 180.degree., a temperature of
25.degree. C. and a rate of 300 mm/min to measure the force
required for peeling. The measurement was made on two samples for
each pressure-sensitive adhesive sheet. The measurement values were
averaged.
Cohesive Force
The various pressure-sensitive adhesive sheets were each applied to
a bakelite plate at an area of 10 mm width and 20 mm length. The
falling (sliding) distance per hour was measured at a temperature
of 40.degree. C. under a load of 500 g. It is generally known that
the smaller the distance is, the greater is the cohesive force.
TABLE 19 Pressure-sensitive adhesive force Cohesive force (g/20 mm
width) (mm/hr) Example 61 533 0.38 Example 62 669 0.32 Example 63
455 0.24 Example 64 635 0.19 Example 65 620 0.33 Example 66 510
0.12 Example 67 673 0.08 Example 68 537 0.09 Example 69 587 0.13
Example 70 590 0.32 Example 71 542 0.56 Example 72 500 0.18 Example
73 520 0.12 Example 74 503 0.54 Comparative 320 0.24 Example 61
Comparative 295 0.11 Example 62
TABLE 20 Pressure-sensitive adhesive force Cohesive force (g/20 mm
width) (mm/hr) Example 75 463 0.11 Example 76 566 0.22 Example 77
275 0.29 Example 78 587 0.17 Example 79 589 0.16 Example 80 531
0.11 Example 81 500 0.17 Example 82 403 0.28 Example 83 421 0.19
Example 84 505 0.08 Example 85 395 0.16 Example 86 411 0.18 Example
87 455 0.22 Example 88 520 0.16 Example 89 480 0.32 Example 90 427
0.26 Example 91 525 0.20 Example 92 453 0.18 Example 93 448 0.26
Comparative 280 0.56 Example 63
As can be seen from Tables 19 and 20 above, all the
pressure-sensitive adhesive sheets of Examples 61 to 93 according
to the present invention exhibit excellent pressure-sensitive
adhesive properties, i.e., great pressure-sensitive adhesive force
and cohesive force while the pressure-sensitive adhesive sheets of
Comparative Examples 61 to 63 exhibit a poor pressure-sensitive
adhesive force.
As described above, the present invention can provide a
pressure-sensitive adhesive composition which comprises as a main
component of pressure-sensitive adhesive a crosslinked polymer
obtained by crosslinking a block copolymer comprising at least two
of a styrene-based polymer block A and an acrylic polymer block B,
e.g., A-B type or B-A type block copolymer or A-B-A type block
copolymer, that has been produced free from the conventional safety
or economy problems in the absence of solvent or in the presence of
a small amount of a solvent to satisfy the desired
pressure-sensitive adhesive properties, particularly well-balanced
pressure-sensitive adhesive force and cohesive force and excellent
heat resistance, in addition to the inherent characteristics due to
the acrylic polymer block B, i.e., enhancing the light resistance,
a process for the preparation thereof and pressure-sensitive
adhesive sheets comprising such a pressure-sensitive adhesive
composition.
* * * * *